If the ban is because of the fact that the customer uses a wheelchair, it's unlawful. See pages 42 onwards of this document (from the Equality & Human Rights Commission):
http://www.equalityhu..._community_sector.pdf
(Some places can prohibit wheelchairs, or limit their numbers, on legitimate health and safety grounds. e.g. because of evacuation difficulties in the event of a fire. But such circumstances would normally only apply to places like historic buildings, where it's impossible to find a way around the problem, rather than to places like community centres).
However that doesn't prevent a ban on grounds that would apply to other users of the centre, if the circumstances were the same. For example, when I worked on the railways, we barred a wheelchair-bound guy from travelling because of his personal hygiene problems. Similarly, when I worked in a pub, we barred a customer in a wheelchair because of his foul language and aggressive conduct.
Chris