I'm an atheist but, even so, I'm concerned that you think 'Catholic' is different to 'Christian'!!!
The Church of England has a presence in Wales. Its rules and procedure are here:
http://www.cofe.anglican.org/lifeevents/weddin gs/
The Church in Wales has information about marriage here:
http://www.churchinwales.org.uk/life/marriage/
The Catholic Church in England and Wales has relevant information here:
http://www.catholicchurch.org.uk/ccb/catholic_ church/how_do_i/get_married_in_the_catholic_ch urch
If you don't truly believe that Christ died on the cross (to atone for your sins), was reincarnated and then lifted up to heaven, you shouldn't be getting married in
any church. (How can you possibly start your married life with a lie?). If you don't
also believe that the Pope is God's representative on Earth (and is completely infallible, including when he says that you should never use any form of contraception) you shouldn't even consider getting married in a Roman Catholic church.
Chris