I don't know UK law, I'm not a legal expert, and I can't give you legal advise. But this article should explain the legal compliance aspects with UK DDA.
You'll see in this article -- and in many others -- that the recurring source on the accessibility requirements for disabled is the W3C consortium's WCAG 2.0 guideline.
Here you'll find the full text of this guideline. I must say that in my personal opinion, many principles in this guideline are far more than disability access. Many remarks are common sense for a good user interface design, and not only for web applications.
This WCAG guideline was in the meantime promoted to international ISO 40500 standard and the European standardization organisations made it to an EN 301549 standard for ICT products and services.
So in conclusion, if you'd follow the WCAG it should help you to ensure accessibility at the large, to justify compliance with UK DDA, but also to claim compliance with several international standards.