To accept credit cards you need a merchant account with a willing bank. These are not that easy to get in the UK. If you don't have a merchant account you need to use a 3rd party to handle the transactions for you. There are lots of options but in essence they will do almost everything for their cut.
The bad news is that:
- even if you have a merchant account it may be against your banks TOS to use it online/card holder not present
- even if they do provide the facility expect to:
- pay an exhorbitant commission rate and
- accept a 60-90-120 day delay before you get the funds cleared.
This is because of online fraud and the high level of chargebacks with card holder not present online transactions. UK banks are also ~5-10 years behind the rest of the world.