Was looking at Charge plug 0 or mango bikes. After a bit of looking around it seems I’d want 4130 frame for a bit more comfort/less weight and if I’m thinking of a mango I might as well go for a Viking citifix for cheap steel singlespeed.
State bike Co have some nice lookers at £400, and just seen foffa on Ubyk for £305. What else should I consider for sub £400?

I’d go straight to LFGSS and ask there. Much better forum for such things:

https://www.lfgss.com/

I wouldn’t bother asking them about Foffa though…

Foffa bikes