Ubigi lists their network (but don't know whether it can be out of date or not)

https://cellulardata.ubigi.com/rates...c-currency=USD

Says 3UK only


There are other providers that have multi network support, but would have a little more latency (exit in Poland or Belgium, believe Ubigi exits in UK or Belgium, and local UK network providers exit in UK but would only have one network). UK network coverage is quite spotty at times even in central london, having more network coverage is good