Normally a foreign card won't work unless verified manually (which OVH often won't do for fraud reasons) since the card billing address has to be set to your UK address.
You just need a UK address and a UK mobile phone number to order. A foreign credit card may work, but you might need to contact support if it doesn't work.
im a swedish guy living in london since a week working.. so i wonder if i will be able to order servers.. still havent got an uk visa though but got uk cellphone..
best regards
micke