The M25 defines the outer limits of London quite well - most of the airports we'd consider "London" tend to be relatively close to it, but could be either inside (Elstree, Biggin Hill, Stapleford, Denham..) or just outside (Wycombe, Blackbushe, Andrewsfield, Redhill...).
If you think of SE England as a region, with London in the middle, the M25 outside London, but a network of roads, railways and airfields throughout the region, you'd be thinking appropriately.
Most of these airports have one or more schools with instruction going on - unfortunately most are poorly served by public transport which may give you problems - but they are served! So being somewhere on the London underground system (which isn't all underground, most countries would call it a "metro") will give you a good chance of travelling to work, whether flying or non-flying. Being on the edges of London is likely to be cheaper. There's minimum wage work throughout the region for EU citizens, particularly in the service sectors which whilst not necessarily much good for aviation, would be good for your English.
As a crude rule of thumb, if an airport in SE England isn't an international airport, but does have an ATZ, there's probably flying training going on.
G