When I had a HUGE flea infestation with my old cat (sadly no longer here) I used Program flea treatment and I treated my whole flat with Indorex spray. The cheapest way is to buy online through one of the major pet companies. I have used Medicanimal several times with no problems.
http://www.medicanimal.com/product/~pro ... tAod7VIAZghttp://www.medicanimal.com/product/~pro ... uct_id=737Program does not kill fleas but needs to be used long term to interrupt the life cycle so you need to kill the fleas that are on him with something like this
http://www.medicanimal.com/setSessionLo ... cale=en_GBYou will also need to spray your entire house, carpets, skirting board, beds etc and the best (most efficient!) way is to remove Kaspar completely while you do it. If this is not possible then you need to do a room at a time but make sure you spray EVERYTHING! Read the instructions on the can before you start and depending on how big your house is you may need 2 cans to do it properly.
Oh, and give everywhere a good hoover before spraying as that seems to disturb them!
It IS possible to get rid of them but will take a bit of work on your part!
Heather