Update on mine (2010 GTi, 71k):
Took it to a local specialist in Edinburgh. Confirmed that the tensioner had failed, and that the timing had jumped six teeth. By some miracle, it hadn't done any serious damage (garage said this was the first in four tensioner failures they'd had that hadn't totalled the engine). It's still showing an Emissions / Engine Management light and throwing a fault code that they couldn't see a cause for (said they'd be happy to explore further, but it would be a lot more labour), but I've done a couple of hundred miles in it and it's running great. Total repair including parts and labour was about £950.
On the downside, my blower motor has since decided this was all far too much excitement and has ceased to function. Also got chastised for the sh!tty oil filter that I'd fitted.