Land costs in the South East of England may be too high, but that really doesn't apply to the whole of the UK...

They are very high in most urban areas where you are likely to have a dev centre.

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.