I can't find one anywhere, despite the wealth of online anorackery when it comes to UK politics. These poeple will probably know (but haven't put anything on their site): http://www.history.ac.uk/hop/
. And this lot have an Enquiry Service: http://www.parliament.uk/directories/hcio.cfm
. Failing that, here's a list of PM's -- http://www.ukpol.co.uk/pm.shtml
--and I'm afraid you're going to have to fill in the missing gaps via Google!