My guess is that they can easily spot that a player is from the UK by checking the currency they usually play. Nobody will use £ unless they live elsewhere and are accustomed to their currency.
Show them your ID, to see what they say. It shouldn't matter that you have a UK passport. The key is that you "don't" live in the UK. How about you went to see your GF for 2 months that live in [country]?
Yeah i tried to give them my i.d and just say i live in the u.k but on holiday playing from abroad, But you cant even select the u.k as a country when trying to send the i.d. That's the issue with trying to send i.d being a u.k player. You cant.