Here are five different UK based companies that all offer accessibility testing services. They all can perform a range of accessibility tests to help you improve your web services, making them more accessible to everyone.
The oldest of the five, at over twenty years, formed in the 1980s and possibly the largest. They are a charity limited by guarantee and have multiple offices across England.
Part of Website Auditing Ltd, a company formed in 2000, based in London England, with a single focus on web accessibility. Has a network of user testers across a range of ages and abilities.
Test Partners Ltd
Another private limited company founded in 2001, also based in London England, with a focus on software and web testing.
Digital Accessibility Centre
A non-profit organisation and a social enterprise, formed around 2012 offering accessibility testing and employs a team of user testers using a range of different assistive technology.
This is the newest of the five, only formed in 2015 and is probably the smallest. With a focus on web accessibility offering testing, training and bespoke services.