[evie2]

Our 4 cats had a really bad infestation of fleas a few years ago.  We sprayed the house, treated the cats with Frontline and used and electronic nit comb to comb the blighters out, worked a treat

[salome2001]

in general: supermarket shelf flea products (Bob Martins etc) are rubbish. Either old drugs with resistance or just no insecticidal ingredients at all! If you don't believe me, look at the active ingredients one day at Tesco.
Frontline or Advantage both work well and are non-prescription.
It is possible for an animal to have an individual reaction (if this happens do remember to tell your vets to fill in a SADR (Suspected Adverse Drug Reaction) yellow form: it's no use just moaning about problems on internet forums. It is also possible for local resistance to develop to one product, especially if used solo for a long time.
The prescription products are not just a way for your vet to hold a monopoly- they usually have additional licences eg. Frontline combo has an insect growth regulator to stop the breeding cycle, Stronghold treats roundworm (helpful if you have young kiddies or immunocompromised people in the household), Advocate is licensed to prevent lungworm in dogs.
You can get cheaper non-POM spottons at Boots or on the internet: what you DON'T get when you save your few pennies here compared to your vet surgery is someone who can give you educated advice about your individual situations: do you have rabbits? How old are the animals? Any skin disorders? Is there now a cheaper generic product that is actually cheaper than buying frontline online?
All products though will not treat a flea infestation in the house- for that you HAVE to treat the house with a spray- every room, every inch of floor, and using the recommended spray coverage. Otherwise all the spottons in the world won;t stop newly hatched fleas ending up on your animal.

[salome2001]

and by the way, you would have been better off spending the couple of quid you spent on the flea collars on a Starbucks cappuccino and pouring it on the cat, for all the good they do in killing fleas. Wish I had a pound for every cat I've seen with fleas merrily sccoting over one of those.