Prima Leisure is the Bailey parts department. Unfortunately they do have a reputation for being a bit overpriced (especially postage) and slow to deliver. You might be better to contact Alde direct - they have a very good reputation for support - and the panel is a simple plug-in. They are at Wellingborough on 01933 677765. This is their
spares web page.
Having said all that, what makes you think you need a new CP? They are normally very reliable. It is possible that the CP board is faulty, but equally it could be the board in the boiler that is misbehaving.
The cable connecting the head to the boiler is a standard RJ45 computer-type cable and could be an issue. If you want to test it first just check the colours in a spare Ethernet cable that I am sure you will have. I suspect the Alde cable will be wired pin-to-pin whereas in a computer patch cable 1 and 2 goes to 3 and 6 at the other end and vice versa (check the colours.) Pin to pin cables are readily available or any small computer shop will make one up for you for a relatively small sum.
There is loads of info in the Interweb (and Alde's site) and lots of YouTube videos to give to guidance. You don't want to spend £200+ and not cure the problem do you?