I know that we have many therapy series members from the UK, so purchasing it from the UK is definitely possible. Perhaps other UK members can speak up here to say how they were able to handle this if there was an issue with the postal code.
I’m not sure this is always true, but I believe most UK post codes are 6 characters in length(?). Make sure you first also change the country when inputing this info, as that will change the fields required. As I may have mentioned to you in your other correspondence, I have a friend who lives in a place without a post code of any kind. When she makes purchases online she just enters some information such as “111111” to fill the required character amount, and her transactions work out. It depends on the card perhaps and the check - for her the other details are enough to prove the transaction is legitimate.