I'd say there are several locations in the UK with quite low costs (definitely massively lower than SE England).
For example Glasgow. Average residential prices are 23% of London, that's a lot cheaper and there's a good level of skilled workforce there.
South Wales where the one of the BA service centres used to be, for example, is low cost and 2 hours train from London (there's Cardiff airport; and St.Athan's [ex-RAF?]).
Land costs are really not high in Birmingham and the Black Country, the second biggest urban area in Britain. You could build within walking distance of (say) Sandwell & Dudley station, with mainline trains to London, for comparative peanuts.
Waterside is absolutely able to accommodate a dev team.