Warning - long long long!
Oh Ellaroo, I feel so sorry - your post brings back a lot of bad memories! We lived in an old house in London, and shortly after moving in we discovered there were rats living under it. It was a miserable time.
There was a problem (can't get technical or specific) with the drains sewers coming from the road to our house. The council pest control responded reasonably promptly ( ie in a couple of days), and put down bait. I think he came back a couple of times, to see if it had been eaten, and replenish stocks, but, they would not remove the dead rats as they were under floor boards).
I was freaking out. I too was a veggie (do they KNOW, or something!) and found the whole situation totally traumatic. I was also really ashamed, so couldn't talk to mum or anyone about it.
Anyway, when they died under the floor boards, the stench was incredible. Dh couldn't smell it at first and thought I was imagining it! Then we were infested by blue bottles. He believed me then. We had several episodes of having to pull up the floor boards in the front room, hunting for corpses. We even had to cancel Christmas (bot sets of parents due to come for the day!) at the last minute - another stinking corpse, and lie to them, pretending we were so disorganised we hadn't done the shopping! Luckily we're so scatty it was reasonably believable.
Anyway, after my tales of woe, some advice :-
You need to find out where they're coming from, eg communal drains like our were. Frankly - don't want to depress you, because hopefully you won't be in the same situation, that problem was not going to be solved with a bit of bait. The whole street was riddled with them. There were gaps in the foundations between the houses, so as well as coming from the drains into our houde, they could run probably the whole length of the street under the floors. there was no way to stop them coming under our house. All we could do was try and stop them coming INTO the house.
To stop them coming into your house you need to go round and block off, with expanding foam filler or anything you can! Get pest control to advise you - any holes or gaps you can find. Look behind units, in the back of cupboards, every inch of your skirting boards for any gaps at all.
Don't leave any food out. This is a drag, but you need to put everything in the fridge or in tupperware. Apparently they especially love dried foods. Another tale of woe. I left a cheese sandwhich in the spare bedroom while I went to our room for something. Came back and found a rat in there! I had a bizarre idea that the problem was restricted to the ground floor, so was totally freaked out to find one in the bedroom. I was also freaking out about our baby! The council couldn't respond just like that. I was too chicken to tackle it, so had to pay about £50 for a private firm to come at once and shoot it! In the hour or so it took for them to come, it has ruined the carpet by scratching and knawing at it to get out. Totally hideous.
We decided in the end, that the problem with dying rats and stinking corpses and lifting the floor boards was worse than them being under the house, so in the end we stopped using bait and concentrated on keeping them out.
I think in our situation the problem would never be solved until the council totally re-did the drains/sewers. Dh's grandad, an expert on all things said that technically the whole street was "unfit for human habitation" because of the victorian drainage system, which aparently would not pass any modern standards.
I was so glad we were moved by dh's firm, and got to leave the house.
Sorry - this may have made you feel 100% worse. i guess moving isn't a logical option! Hope at least a couple of points prove useful. The very best of luck.