I'm experiencing what looks like throttling too.
iPlayer test results are 8Mb on everything but streaming 2 which is at 1Mb. If I start downloading from usenet it'll cap at 100-120KB/s and the streaming 2 test result will drop to almost nothing so there's definitely something going on with non-standard ports - I've tested this a few times now and it's been consistent.
It also shows in the TB speed test, this is with nothing else running and the different between port 80 and port 8095:
I hope it gets sorted soon, I really can't be bothered with looking for another ISP when up to now they've been fine.