x-post: foreign SIM in UK locked mobile?

[Satsuma]

Cross post to get help with one element of my query: whether a UK locked mobile can be used with a foreign SIM?

I was wondering if the UK networks "partner" with carriers overseas; or whether it would be UK Vodafone/EE/whatever" and that's it, no other carrier anywhere at all.

Any replies on the OP if you'd be so kind: viewtopic.php?f=38&p=235583#p235583

TIA
Sats