Well it's all sorted now, thanks to everything that is Good and True.
The colleague in question offered a full apology and the issue is now resolved.
In the end it didn't spread to HR and Occupational Health, which was my decision. The issue has stayed within the team, and my team leader has promised to be on it should it arise again.
I ended up being signed off sick with work related stress for the first two weeks of the year. Between Christmas and NYE I unfortunately started experiencing some psychotic symptoms, which was obviously very worrying. I saw my GP and she signed me off, as well as increasing my medication. I am feeling much better now.
I have been back at work this week, and all is (relatively) well. It will take some time to rebuild trust, but the signs are promising.
Thanks for all your support.