Web design

Website optimisation checklist: your 2026 UK guide

Elevate your online presence with our comprehensive website optimization checklist for 2026. Improve speed, compliance, and accessibility today!

Mateusz SalkowskiHead of Web Development, AMW Media

Published 19 July 20269 min read

Web design

TL;DR:

Focusing on page speed, Core Web Vitals, cookie consent, accessibility, and monitoring ensures your website outperforms most competitors.

Regularly test and optimize images, implement caching, and minimize resource sizes to achieve better loading and responsiveness scores.

Your website optimisation checklist, at its most useful, comes down to five things: page speed, Core Web Vitals compliance, UK cookie consent, accessibility, and ongoing monitoring. Get those right and you are ahead of most of your competitors before you have even touched your content.

Here is what the checklist covers at a glance:

Speed: target a page size that aligns with Google’s performance best practices for faster loading, compress images, and use a CDN
Core Web Vitals: LCP ≤ 2.5s, INP ≤ 200ms, CLS ≤ 0.1 (all measured at the 75th percentile of real-user sessions)
Cookie consent: active opt-in for all non-essential cookies, per ICO and PECR requirements
Accessibility: mobile-friendly consent banners, readable text, clear navigation
Monitoring: retest after every change using Google Search Console and PageSpeed Insights

One figure worth keeping front of mind: Google’s “good” rating depends on the 75th percentile of real-user data, meaning a small cluster of slow visits can drag your entire score into the “Needs Improvement” band even if most users have a fine experience.

Your website optimisation checklist for speed and Core Web Vitals

1. Understand what Core Web Vitals actually measure

Google’s three Core Web Vitals each target a different part of the user experience. LCP (Largest Contentful Paint) measures how quickly the main content loads. INP (Interaction to Next Paint) measures how fast the page responds to a click or tap. CLS (Cumulative Layout Shift) measures visual stability, specifically whether elements jump around as the page loads.

Metric	What it measures	Good threshold	Needs improvement	Poor
LCP	Load speed of main content	≤ 2.5s	> 2.5s and ≤ 4s	> 4s
INP	Responsiveness to input	≤ 200ms	> 200ms and ≤ 500ms	> 500ms
CLS	Visual stability	≤ 0.1	> 0.1 and ≤ 0.25	> 0.25

To pass the Core Web Vitals assessment, all three metrics must meet the Good thresholds based on the 75th percentile of real-user sessions.

2. Prioritise field data over lab data

PageSpeed Insights gives you both lab data (a simulated test) and field data (real visitor experiences). Lab data is useful for debugging, but when the two conflict, field data should guide your priorities. It captures actual devices, network conditions, and user behaviour that a controlled test simply cannot replicate.

Top-down view of web performance testing tools on desk

Pro Tip: If your field data shows “Good” scores but your lab data flags issues, do not panic. Focus on field data for ranking decisions and use lab data to investigate specific technical problems.

3. Compress and properly size your images

Large, uncompressed images are the most common cause of poor LCP scores. Compress your existing media library, use modern formats where supported, and make sure images are not uploaded at a larger resolution than they are actually displayed. For WordPress sites, an image optimisation plugin handles this in one pass.

One caveat on lazy loading: it is worth enabling for images further down the page, but exclude the hero image at the top. Delaying the element that determines your LCP score works directly against you.

4. Set up caching and use a CDN

Caching stores a ready-made version of your pages so the server does not rebuild them from scratch for every visitor. A content delivery network (CDN) serves those cached pages from a location closer to the visitor, cutting response time further. Together, these two changes often produce the biggest single jump in LCP scores for sites that have not implemented them yet.

5. Minify CSS and JavaScript files

Render-blocking CSS and JavaScript files delay the browser from displaying content. Minifying these files removes unnecessary whitespace and comments; deferring or asynchronously loading non-critical scripts means the browser can start rendering the page without waiting for them. This directly improves both LCP and INP.

6. Keep page size below 500KB and limit resources

Google’s own guidance recommends keeping total page size below 500KB and limiting a page to 50 resources for best performance on mobile. Both targets are achievable through image compression, removing unused plugins, and auditing third-party scripts such as chat widgets and analytics tools.

7. Retest after every change

Fixing one metric can accidentally worsen another. After each technical change, retest your Core Web Vitals in Google Search Console to confirm the improvement held and nothing else regressed. The Search Console Core Web Vitals report groups URLs by issue type, so you can see exactly which pages still need attention.

UK cookie consent law sits under PECR (Privacy and Electronic Communications Regulations) and UK GDPR, enforced by the ICO. The rules are clear: you need active, informed consent for any cookie that is not strictly necessary. Silence, inactivity, or pre-ticked boxes do not count.

Use this checklist to audit your current setup:

Audit every cookie your site sets and confirm its purpose
Remove any cookies you no longer need
Identify which cookies are strictly necessary (exempt from consent) and which are not
Implement a consent mechanism that requires a positive opt-in action before non-exempt cookies are set
Provide clear, granular options so users can accept or decline by category
Disclose the identity of any third parties whose cookies you use
Record consent and make it easy for users to withdraw it at any time
Review your consent setup whenever you add new cookies or change their purpose

The ICO is explicit that consent requests must not unnecessarily disrupt the user experience, but avoiding disruption does not override the need for valid consent. Some friction is legally necessary.

Pro Tip: Use a Consent Management Platform (CMP) to record user preferences accurately. If you ever face an ICO audit, that record is your evidence that consent was properly obtained.

Accessibility and UX checks that support compliance

Accessibility and legal compliance overlap more than most people realise. A consent banner that is technically present but impossible to read on a small screen does not produce valid consent under UK law.

The ICO is direct on this point: if a banner is hard to use on mobile, any consent gathered through it may be invalid. That makes mobile usability a compliance issue, not just a UX nicety.

Work through these checks as part of your regular website performance audit:

Test consent banners on multiple mobile screen sizes and confirm buttons are easy to tap
Check that banner text is readable without zooming
Verify that “accept” and “reject” options are equally prominent (a tiny grey “reject” link next to a bold “accept” button fails the ICO’s expectations)
Run Google’s Mobile-Friendly Test on your key pages
Check colour contrast ratios on all text, including within consent pop-ups
Test keyboard navigation across the site for users who do not use a mouse
Confirm that images have descriptive alt text
Integrate these checks into your standard UX review process rather than treating them as a one-off task

The practical rhythm that works well is to run a full accessibility and consent audit every quarter, with a lighter check after any significant site update.

How AMW Media supports website optimisation and UK compliance

AMW Media’s team holds certifications across Google, Meta, Shopify, WordPress, and Framer, which means the advice you get is grounded in the actual platforms your site runs on, not generic theory. The team covers web design, SEO, content production, and PPC, so performance improvements get joined up with the broader marketing strategy rather than treated in isolation.

For 2026, AMW Media’s guidance for UK businesses covers:

Core Web Vitals audits with field-data-led prioritisation
Technical SEO fixes including crawlability, canonical tags, and mobile indexing
Cookie consent implementation aligned with ICO and PECR requirements
On-page SEO structure: title tags, H1 alignment, internal linking, and schema
Ongoing monitoring via Google Search Console with monthly reporting

If you want a site that performs well in Google Search and holds up under an ICO audit, the two goals are more connected than they appear. AMW Media’s web design and SEO services are built around that overlap.

Ready to put this checklist into practice? AMW Media’s SEO and performance team can audit your site, identify the highest-priority fixes, and handle implementation so you are not left guessing which change made the difference.

Key takeaways

A complete website optimisation checklist covers Core Web Vitals, UK cookie consent compliance, mobile accessibility, and regular retesting after every technical change.

Point	Details
Core Web Vitals thresholds	LCP ≤ 2.5s, INP ≤ 200ms, CLS ≤ 0.1, all measured at the 75th percentile of real-user sessions.
Field data leads decisions	When lab and field data conflict, field data reflects actual user experience and should set your priorities.
Cookie consent must be active	ICO requires a positive opt-in action before non-exempt cookies are set; silence or inactivity is not valid consent.
Mobile usability affects compliance	A consent banner that is hard to use on mobile can invalidate consent under UK law.
Retest after every change	Use Google Search Console to confirm improvements held and no other metric regressed after each fix.

FAQ

What are the Core Web Vitals thresholds for 2026?

Google’s passing thresholds are LCP ≤ 2.5s, INP ≤ 200ms, and CLS ≤ 0.1, all assessed at the 75th percentile of real-user sessions. All three must hit “Good” for a page to pass the Core Web Vitals assessment.

No. Strictly necessary cookies are exempt under PECR. All other cookies, including analytics and advertising cookies, require active, informed consent from the user before they are set.

How often should I run a website performance audit?

A full audit every quarter is a practical baseline, with lighter checks after any significant site update, plugin change, or new third-party script addition.

What is the difference between lab data and field data in PageSpeed Insights?

Lab data comes from a controlled simulated test; field data reflects real visits from actual users on their own devices and networks. Field data is the more accurate measure of what your users actually experience.

Yes. The ICO states that if a consent banner is difficult to read or interact with on mobile, any consent gathered through it may be invalid, exposing you to potential enforcement action under PECR.

Website optimisation checklist: your 2026 UK guide

Your website optimisation checklist for speed and Core Web Vitals