I've been having the same problems recently. Last night somthing strange was going on. Usually my ping to bbc.co.uk is around 20. Last night it was 300-800ms! I also pinged each hop and it seems the problem is with the first murphx hop.
I have used the BT test site but predominately the speedtest.net site as it is quicker. The BT test usually has me waiting for a couple of minutes and then often times out.
On all the tests my ping is consistently 80-100ms. The up link speed is consistently 0.5Mb/s to 0.6Mb/s no matter if my download speed is 4.8Mb/s or 0.3Mb/s.
My exchange VP is and has been consistently green.
I am coming to the conclusion that it is a ISP bandwidth problem although ADSL24 tech support have told me they have been unable to detect any problem.