FTTC download speed of 19MB should be over 70, upload ok...

[#1]

I switched to 76MB fibre over a month ago and was initially getting about 72MB upload speed.  I noticed about 10 days ago that this had fallen to under 20MB. Upload speed is still decent at around 18MB.  I have tried disconnecting and reconnecting, rebooting router without success. No apparrent noise on the line.
Any suggestions?
Thanks
Info below:
Plusnet:
Estimated line speed:
72Mb (Accurate to within +/- 1Mbit) - Checked on 2012-08-22 15:25:55
Current line speed:
19.3 Mb
BT Speedtest result this morning
Download speedachieved during the test was - 17.82 Mbps
For your connection, the acceptable range of speedsis 12 Mbps-77.43 Mbps .
Additional Information:
IP Profile for your line is - 77.43 Mbps
Upload speed achieved during the test was - 16.86Mbps
Additional Information:
Upstream Rate IP profile on your line is - 20 Mbps

[#2]

Hi nstone,
I've adjusted your profile to match your sync speeds. Let me know how your get on.
Chris

[#3]

Chris,
Many thanks for your speedy reply.  I'm now getting test results in the range 55-72MB, so much better!
Neil