Where to invest as a non British citizen?

Well I live in €uroland so for me "money" equals €uros; I've had a decent year in UK p2p, and yet I've actually lost money because of the decline of the £

OK then,
You will need a UK bank account for some UK (GBP) platforms. and I wouldn't be surprised if they wanted to see an EU or UK passport, but I live outside UK and you can have accounts with :
ABL AC FS L MT RS REBS  (and cannot have accounts with FC, Z)
Abundance,Archover, Bondmason, FE, FK, GrowthSt, Justus, Landbay, LC, LW, Orchard, Proplend Relendex TC, Wellesley, Wiseapha
and cannot have accounts with LI

In €uroland possible are Lendix?, Ecrowdinvest, Investly, Twino, Mintos, Linkedfinance, Loanbook.es Comunitae.  I've never found a German platform to take me.  
There are lots of French platforms, I can't say if they would take you if you live outside France, many of them don't take security and do list near startups.  There is a list here: www.crowdlending.fr/comparatif-des-plateformes-de-pret-pour-les-entreprises/     If you have the French crowdlending.fr is the equivalent of this place and the agregateur has discussions on each new loan

Note I make no comment as to which platforms I think are OK and which are not.