We treated our dog with Frontline (onto the skin at the back of her neck) last week but yesterday I found a flea hopping around on our sofa!!
I realise it could have come in from garden (or anywhere) as we had just been playing football outside but am wondering if I need to treat her again or do I need to treat the furniture? Any ideas? I haven t seen anything since but can t help scrathching when I sit on the sofa!!

There are 80% more fleas in various stages of development in the environment (more indoors than out!) than there are on a dog, so if you've ever found a flea on your dog (or cat) you'll need to treat the whole house as well as the animal. Hot-wash all the dog's bedding and spray soft furnishings and carpets with a reputable product, paying extra attention to around skirting boards.

Flea lifecycle.

Any recomendations on which product to use?

'Acclaim' has had good reports. More information here.

indorex is also good

That's an interesting link JG. 

In about 10 days the pupae develop into adult fleas which can remain in the cocoon (where they are resistant to insecticides) for up to 5 months.

I was always told 'in the old days ;)' to give 2 treatments, 10 days apart to interupt the production cycle.

Treat the sofa.   If your dog had fleas they and their eggs could be anywhere - soft furnishings, rugs, the dog's bedding.   Obviously, also check your dog.  I'd ask the vet if you find fleas before giving her another dose of something.

I believe Frontline make two version of the topical ointment.  One will just kill adult fleas and the other version (contains S-methoprene) kills adult fleas and their eggs. The latter is obviously better, since it prevents the eggs already on your dog from hatching and jumping off her coat onto something more hospitable (like you or your sofa).

If you have carpeting you can put a flea collar or a flea powder in the dust bag or canister.   It will kill the flea eggs and any live fleas you pick up.  Of course, if you have a Dyson or other make without dust bags the best thing to do is empty it after every use.

And also treat the inside of the car (if the dog travels in it). :)

out of all the products available I prefer acclaim also it doesnt smell to bad remember to spray around the skirting boards.