European ITSP With UK (London) phone numbers

we have US customer that is opening an office in London and has requested that we setup a london number for them and initially forward it to the employee cell phone. i am looking for a recommendation for an ITSP that can provide this simple service. I have tried SIPgate but they require that you log into their system from a UK IP Address in order to get UK landline numbers. I tried Goldfish in Ireland but they require a UK or Ireland credit card. if anyone has a recommendation i would greatly appreciate it?