There are two sides of the story for disabled access on buses. It is important that everybody is able to board a bus and travel, but this means withdrawal for step-entranced buses. I found out about the regulations from a photographer on flickr. I was at the time shocked to hear that some of my favorite buses would have to be withdrawn by 2016. Anyway, here is the article on the British Government's site.
When will all buses and coaches meet PSVAR?
All full size single deck buses over 7.5 tonnes will be fully accessible from 1 January 2016, and all double deck buses from 1 January 2017. New buses weighing up to 7.5 tonnes and coaches will be required to have wheelchair access from 1 January 2005. All buses weighing up to 7.5 tonnes will be fully accessible from 1 January 2015 and coaches by 1 January 2020.
Source - gov.uk/government/publications/bus-coach-accessibility-faq
When will all buses and coaches meet PSVAR?
All full size single deck buses over 7.5 tonnes will be fully accessible from 1 January 2016, and all double deck buses from 1 January 2017. New buses weighing up to 7.5 tonnes and coaches will be required to have wheelchair access from 1 January 2005. All buses weighing up to 7.5 tonnes will be fully accessible from 1 January 2015 and coaches by 1 January 2020.
Source - gov.uk/government/publications/bus-coach-accessibility-faq