Okay have looked and it looks like it was working for you on http://www.thinkbroadband.com/speedtest/results.html...
7th March, but misbehaving on 16th http://tbb.st/142650351972134611609
Does the upload stall for around 90 seconds before traffic starts moving in the upload direction? And were the tests done on the exact same PC?
The flash test which is what you are using has not had any changes for many weeks, hence asking the http://labs.thinkbroadband.com/speedtest
version is the one that is having a lot more changes made. So immediate presumption was we had broke something, but looks more likely that this may be a AV issue.
We are not using HTTP for the upload in the flash test, but a custom protocol over TCP port 8095 which now and then draws ire from some AV suites. Looking at the most recent 100 Virgin Media users today you appear to be the only one with this problem. Others are getting the 3, 6 or 12 I'd expect.