If you are able to use a nit/flea comb on your kitty - have a bowl of water handy and squirt a few drops of Tesco Value washing up liquid into the water. You only need to add a little, no bubbles is best so add to the water instead of the other way around....It has to be the really cheap own brand stuff.... 35p job. One you capture a flea using the comb, drop it into the solution and leave it whilst you continue to comb, checking your cats arm pits and under the chin as these seem to be hot spot areas for them.
Not sure why, but whatever is in the washing up liquid kills the little fuckers almost instantly! Highly satisfying and addictive plus my cats love a good grooming session!
(Doesnt have to be tesco washing up liquid of course, wherever you shop is bound to have their own cheap stuff)