I think there is one important factor which I would like to add to this thread.

Life had reached the stage where I needed / wanted to upgrade from flat to house about 18 months ago. I would have loved to have stayed in FH. Since I bought in 2001, however, FH had gone from a void unknown outside locals to ironic beard central (or should that be central?). Given it had gentrified, hey presto, house prices were out of my budget.

Hence the solution was to move somewhere which yet to gentrify and I duly found a lovely 3 bed in Catford for £350k.

For those who bought in FH pre 2010, things have changed. This has been happening all over London for decades. When I first came to London in the mid 90's my mother was horrified I was considering living in Clapham Junction as it had been full of undesirables in her day. Why couldn't I live in Earl's Court or South Kensington? Riiiight mother. Things have changed a bit since your day.

To say you require a £400k mortgage is a bit far. You will if you want to live in FH. Assuming you made some money on your current home you should be able to upgrade with a £250k mortgage, just need to move out a little further.

As for moving out of London... maybe one day. I once commuted from outside London and frankly the longer I can postpone going back to that life the better.