In the UK you have to conform to the Disability Discrimination Act (DDA), and essentially it sets out guidelines for what you should be doing and which standards you should be meeting etc.
Essentially it comes down to these four things:
Minimum of WAI Level 1
EU recommendations of WAI Level 2 compliance
And as much of WAI Level 3 as you can
Preferably make sure you conform with Section 508.
For a brief explination (without actually going through hundereds of pages of the DDA), read the section titled 'What does the Disability Discrimination Act (DDA) state?' on the Web Credible article (below).
The DDA is based upon the UK's politicians interpretations of the current laws ... when dealing with technology you should assume the politician knows less than your grandmother.
There is a fuzzy law that says something like 'websites must be accessible' . No one really knows what that means in the UK. If you aim for 508 (its not perfect, but there is no better standard atm) you will surpass current UK and EU regulations regarding accessibility rules.
For our policy: http://www.w3.org/WAI/Policy/#UK the 508 is not a UK standard and Bobby is a moronic robot that will give you false results. Like was stipulated WAI-A is very desirable and should be reached.
You cannot usually meet Triple-A in "reality" it's a 'holy grail' type thing - theoretically you can but most sites that are labelled as such aren't - your best bet is to strive for double-AA and some of AAA.
That will get you part of the way there is no actual body or 'validator' you have to make educated judgement calls and test using various methods and scenarios with real people that may have disabilities, etc.
That's what I did with: http://www.xhtmlcoder.com/worthvalley/ if you want to be ultra strict at interpretation it could be considered a different level. Basically you have to learn that it's not all about checkpoints.
I guess there is only so much that we should trust from robots.
exactly...they're a tool, but an essentially dumb tool. you could put an alt="chicken" on all your images, and bobby-like checkers would likely give you a thumbs-up. by all means, use it an automated check as a starting point, but always back it up with human checks.