What applies
The United Kingdom is outside the European Accessibility Act, but the Equality Act 2010 requires service providers to make reasonable adjustments, and web accessibility claims are brought privately. A UK store that sells into the EU is still within EAA scope for those sales.
The UK is outside the EAA, but the Equality Act requires reasonable adjustments for services, and claims are brought by individuals with no statutory cap on damages. UK stores selling into the EU are still in EAA scope.
Penalties
The ceiling in United Kingdom is Uncapped damages. In practice enforcement usually begins with a complaint, followed by a requirement to remedy within a stated period; penalties attach to failure to act rather than to the first finding.
Who is in scope
Any provider of services to the public. There is no turnover threshold and no microenterprise exemption.
What to do about it
The technical test in both cases is WCAG 2.1 level AA. Run the scan, fix the ranked findings, and keep the dated report as a record of what you identified and when. Automated testing covers part of the standard; a full assessment needs a qualified auditor.