Possible fleas :(

Gizmo has been staying at my OH's with me for the past week, and has had his first encounter with another animal, my OH's cat. Charlie (the cat) has a flea collar, but we think he has fleas, as he has been scratching like mad. We've been keeping him out of the bedroom as its where Gizmo has been sleeping, but we think he may have passed them on. I haven't seen any fleas on gizmo, but then I don't really know what i'm looking for! I bought some Johnsons veterinary insecticidal spray extra for small animals, which is supposed to kill fleas, lice and other common external parasites. (http://www.amazinganimal.co.uk/insecticidal-spray-extra-p-22536.html)
Is it going to do Gizmo any harm if I treat him with the spray even if he doesn't have fleas? Because I am like a walking flea bite at the moment (i must have really tasty blood, because no-one else even has one!) So i really want to get to the bottom of the cause!

Flea collars don't work, so the cat probably does have a flea problem.

The best flea treatment for rabbits is Advantage, which is only available from vets (or from a pharmacy if your vet will give you a prescription).

You will also need to hoover the house throughly and treat carpets/floorboards, skirting boards and furniture with a household flea spray.

BTW the best way to test for fleas is to flea comb the animal onto some white paper and wet any spots of dirt. Flea dirt will turn red.

You can also place electric flea traps (available on ebay) or bowls of warm water around the house to see if you catch any critters

I was also told Johnsons doesn't work so I purchased some spray from the vets can't remember what it was called (endurex) or something like that and it worked a treat. It was only for use in the house though and not on the rabbit (I treated him separatley).