PumpkinsMummy I like your thinking, but having spoken to the neighbours I am pretty sure they are not the suckers on your wineglass type of people, whereas we most definitely are. The vet kept it in a little bag, and I definitely recognised it as one of ours.
In terms of bills, we will just have to suck it up. I think we are at about £710 so far. I have no idea how that compares with other vets.
We have been having regular updates from the vet, and I visited her yesterday. She is doing well, and in very good spirits, although only ate anything for the first time tonight. The vet has warned that she will need close monitoring for a week after the surgery before she is free of the risk of complications.
I have posted before about these neighbours who were trying to lure her away. She completely changed last summer - became distant with us, and started staying out overnight, sometimes for days at a time, and when she did come back, she would be smelling of perfume! We put a collar on her, with a name & address tag; and when that made minimal difference, we put a locate tracking device on her collar, which has made a bit of difference, but not much.
I had to go knocking on their door on Thursday to get her, so I could bring her to the vet on Friday morning. When they answered, I asked if they would mind checking their garden for her, as she was very ill, and they said she was in the house. I went in, and there she was, sitting in their living room, looking absolutely awful. There was no way they couldn't have noticed that she was so ill, yet they were keeping her in their house.
They started trying to justify why they had her in their house (oh, she loves coming in, she's very charming, she doesn't seem to like her sister (actually her grown up kitten, but anyway), we saw on TV that cats are solitary creatures and don't like living with other cats, yada yada
). Basically, they are reaping all the benefits of owning a pedigree cat without any of the responsibility or bills. 
I think I will drop a note to them stating that she will require very close monitoring after her (expensive) major abdominal surgery, and please would they ensure they don't feed her or allow her into the house, especially not overnight.
We will hopefully get her back home tomorrow evening. The poor thing has a scar the entire length of her tummy. The vet had a feel around, and they are pretty sure there are no other sucker things in there.