Too late. I saw them in my garden in Winchester. Apparently when the old Workhouse in Winchester was converted into flats and houses, the sewage pipes had to be replaced and the whole of Winchester was suddenly overrun with giant rats. A couple of years later, the prison half a mile away had two new blocks built and the problem happened all over again. My house was halfway between the two, and we were still connected to the ancient pipeworks. My neighbours warned me, I was sitting by the window one day and I saw two huge rats playing on the patio. I put down loads of poison, nothing seemed to stop them and others appeared. In the end the Rentokil man was called out and a huge nest was discovered under next door's decking. All the time they were warning me, they were standing on them! Definitely small cat sized but with shorter legs. I picked a dead one up that was lying in the garden and it was very heavy.
To be fair, the warnings about it have been out there for years. As a gardener, we certainly knew about it, since rats eat people's veg as often as any pigeon or rabbit. But unless you go to a country store and buy the poison in bulk it is very expensive, so people don't keep it up. They use it once or twice and so the animals recover and develop an immunity. The rats in Winchester weren't dying because I thought I was killing two, so putting down enough I thought. In reality, I was probably dealing with over a dozen.