The ABPS is formed for delivering an information service to local societies, Specialist Societies and to work alongside Dealers throughout the UK.
Unfortunately, ABPS is unable to advise directly on the sale of stamps and postal history. We would suggest that you should seek the opinion of an expert and they can be found at the Philatelic Traders Society. A list of their members is on their website thephilatelictraderssociety.co.uk
There is some useful advice on the site that you can read before contacting anyone. The alternative is to contact a philatelic auction house near you and get their opinion.