A mate got a spray thing (like the room deodorisers) that sprays some hormone that is meant to calm cats down. It replicates the hormone that cats release when they are pregnant. Might be worth trying.
Thanks HotI, we've done the spray thing in the past to try, but they dont seem to work on our animals! Instead of deterring them, the cats want more of the smell and think we are encouraging the behaviour! " the dog is the same unfortunately!

Thanks Tasha, I'll make up some ads to put round the vets too. I messaged DH at work and asked him to start asking round to see if anyone will take her. Theres a fair few animal lovers at his work, so hopefully someone will take him up on the offer!