There is a new electronic access to UK treaties

"UK Treaties Online:
This new service enables you to access details of over 14,000 treaties http://www.fco.gov.uk/en/treaties/search involving the UK. Our treaty records are based on information received by the FCO Treaty Section over many years. You will be able to research the existence of treaties, obtain key information about them (such as place, place of signature and entry into force date) and see which States or organizations participate in them."

  Here is the address: http://www.fco.gov.uk/en/about-us/publications-and-documents/treaties/uk-treaties-online/