There are regulations and laws relating to whether you can pick and choose your customers and how you treat certain categories of guests. It is also important to remember that once a booking has been agreed with a customer a contract exists in the eyes of the Law. This contract cannot be changed without the express agreement of BOTH parties.
If you take chance customers (this does not apply if you only ever take pre-booked guests) you can only refuse to take a guest if
You cannot refuse to take a guest (subject to availability of a room) on the basis of disability, age gender or race. If you provide any sort of accommodation, serviced or self-catering, the Equality Act 2010 applies to you (this act replaces the Disability Discrimination Act).
The Home Office in August 2012 issued a new guidance document, which details how new provisions mean you cannot discriminate against customers because of age. See the link on the right.
The Equality and Human Rights Commission also has online information. See the link on the right.