In reply to James Malloch:
I think doing the self assessment form yourself would be the way forward. Just take your time and google things you don't understand.
One of the first parts of the form will ask you "did you do think thing you've never heard of and don't know what it means". After a quick google, you realise it's not relevant to you, so you click no, and then the form gets much smaller and will then be limited to your pension contribution bit.
Bits that nearly caught me out.
When you enter the amount you paid into your pension, divide it by 0.8 if you paid into a SIPP, as it explains in the instructions it wants the amount paid into the SIPP, not what you paid in. I,e, include the government 20% top up.
It then asks you to enter it again using similar wording and it took me a while to work out what the difference was. In a nut shell, it's trying to establish if the amount you paid into the SIPP is a one off payment or a regular payment. If regular, they may adjust your tax code.
I entered the same value again as I want my tax code to remain unchanged.
The rest of it was straight forward and probably only took 20 minutes.