I like this plan as I think it is inflation proof, the only way I see that it could fail catastrophically is if the price of housing everywhere else rises much more then the price of housing in London, trapping me in the house.
The price of housing in areas which are not easily commutable into london (or other big city) will always be much lower than in commutable areas.
Nothing is going to change that.
So I’d say you are right as long as you are happy with moving to such an area.
I guess the question is what shape will the housing market as a whole be in when you decide to cash out? If the whole UK housing market has collapsed massively then you might get a lot less than you think.
My personal (completely uneducated) opinion is that a long-term collapse will not happen. Prices in London and the SE will have to level off at some point but I think will always remain high within our lifetimes.