Hi anyone got any ideas. My cat is 18 and over the last month or so has got into the habit of constantly licking her bottom. We dont think its worms as she is a house cat fro choice and very rarely goes out.

she probably has a blocked anal gland. if she's also licking all around, to the extent she's removing fur, she may also have a touch of cystitus. One of my girl cats suffers.
The vet will clear the glands if you don't fancy doing it yourself with a tissue. You need to be quite firm.

She is getting on in years now and may be a little incontinent.

Good sensible answer, it's almost always something minor that can be treated in one visit.