Various sites, contacts and places that ixies find useful.
Beach's Motorcycle Adventures: http://www.beachs-mca.com/
Bike Tours UK: http://www.biketours-uk.com/
£50 a day seemed to be the average for a non-sports bike back when I last looked. (From Craig Miller, posted 27/07/2009)
Mentioned by someone, no endorsement:
When asked why they didn't cover touring motorcycles (over 125ccs) on their otherwise good (i.e.: covers caving and canyoning) travel policy, a 'major insurance company' apologised and (off the record) recommended this mob, with whom they are NOT affiliated.
So these are the motorcycle travel insurers what the Insurance Industry use: