Thanks T and Brendan.
For OT reasons, I'm going to submit my 2014 tax return on 1st Jan 2015. I've paid my preliminary 2014 tax, along with what I owed during 2013 - so hopefully it won't be a massive shock. Because I need to get my self assessment info pronto for 2014, do you see any road blocks for doing it so early?
Normally I get my accountant to file it, but I'm well able to, so I think the 'filling out' part should go ok.
It's crazy that 58,000 files were uploaded on the final day this year. The software must be very resilient to crashing!