Most of what you ask is either in JAA-FCL 1 which is the licensing bible or available on the CAA SRG web site in the form of a Policy Update or in GIDs (General Information Documents). Here's a good link
CAA GID
An IR revalidation (or renewal if you've let it lapse) on a twin is valid on a single but not vice-versa. Also IRs on multi-pilot aircraft are not valid on single pilot aircraft. Differences training on a twin would be valid for the same differences on any single and are valid indefinately on singles but only 2 years on a twin unless you keep in practice on the type.
[ 09 December 2001: Message edited by: Stan Evil to add link and get info correct ]
[ 09 December 2001: Message edited by: Stan Evil ]