Super easy. I got an online export permit from the DTI and it cost me nothing. This also allowed me to bring it back when I returned to live here so that I avoided import duty. I think the DTI has changed its name today.
As a side note, I was told that I had to surrender my FAC when I left the country, they asked me to post it back once I was abroad. When I returned to the UK, they admitted that had been an error and I was entitled to keep it so don’t give it up so easily if you might return before it expires.