Pruning a tree - how to find out who legally owns it?

There's a massive chestnut tree (London) in a garden that backs onto mine. It may well pre-date when these houses were built in the 19th century. The previous owners of that garden kept it in 'check' - and myself and other neighbours contributed to that cost. That house was sold a few years ago and converted into flats. Since then, it's grown considerably. A letter drop to them asking about who is responsible for it not replied to. It is overhanging my garden quite a bit now - and stops most of the light to it too. Making my old apple tree unhappy. Also blocks my satellite dish - although that's not a real problem these days.