Changing people's behaviour, not killing the cats
I'm filling out some surveys by students today on different aspects in relation to community cats and donations to animal welfare among others. One interesting thing that struck me as I was filling out one of the questionnaires was this - I wonder how many cat complaints actually arise because people cannot or do not want to talk to their neighbours.
The thing is that for people who complain about cats, something CAN be done about them. When you complain to town council, the cats are just removed. If you don't want to confront your neighbour though (and a surprising number of people are unwilling to do so), then you can't change your neighbour's attitude.
Of course, I am discounting those people who have tried to talk to their neighbours and whose neighbours are not responsive (and even then CWS can help with mediation in cases like those). However, if your neighbour is feeding messily, or letting their cat out of the flat, why not first try talking to THEM? If you can change their behaviour, then the problem goes away. Trapping the cats does not solve the problem, because if your neighbour's behaviour is causing the problem (for example, letting their cats out, or feeding in an irresponsible manner), then the problem will reoccur because your neighbour will continue doing what they have been doing all along.
Removing cats and killing them has a very short-lived effect because new cats move in due to the vacuum effect. Getting to the root of the problem will get rid of the problem, without having to get rid of the cats.
An added bonus in some cases is a better relationship with your neighbour because you went and talked to them - not complained behind their backs to the authorities.