Solid connection but poor web browsing and streaming video stutters

[#1]

I've not got the fastest connection ( it was about 2mb but after a recent engineer visit it went up to 3mb).  Since the visit and new face plate the line is very stable, drop outs are very rare.  And up till last week web browsing, downloading files and streaming video all worked well.
But this last week web browsing has been very slow at times, video playback barely manages 10-20 seconds without needing to buffer and when files are downloading they do the quick step (fast fast slow slow fast slow) and sometimes the download seems to hang for several seconds at a time.  Yet I seem to be synced up at a decent rate and my BT profile is 2.5meg which should be fine.
I've tried rebooting the router once to see if it made a difference but it didn't.  I've run a BT speed test which said to flag the issue up.  Seems to be better during the day and worse at night so I don't know if its just the exchange being busy or a problem with the line.  Could someone advise if there is anything I should try?
Router Stats, BT Speed test and Current Line Speed
Router Info
Uptime: 2 days, 19:36:40
DSL Type: G.992.1 annex A
Channel mode: Interleave
Maximum Bandwidth (Up/Down) [kbps/kbps]: 648 / 3,520
Bandwidth (Up/Down) [kbps/kbps]: 448 / 3,456
Data Transferred (Sent/Received) [kB/GB]: 0.00 / 2.20
Output Power (Up/Down) [dBm]: 12.0 / 18.5
Line Attenuation (Up/Down) [dB]: 31.0 / 59.0
SN Margin (Up/Down) [dB]: 11.0 / 6.5
Vendor ID (Local/Remote): TMMB / TSTC
Loss of Framing (Local/Remote): 72 / 0
Loss of Signal (Local/Remote): 2 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 131,072 / 0
FEC Errors (Up/Down): 658 / 7,446,131
CRC Errors (Up/Down): 95 / 1,218
HEC Errors (Up/Down): 62 / NA

Bt Speed Test Results
. Best Effort Test: -provides background information.
Download  Speed
2.36 Mbps

0 Kbps 7.15 Mbps
Max Achievable Speed
Download speedachieved during the test was - 2.36 Mbps
For your connection, the acceptable range of speeds is 600 Kbps-7.15 Mbps.
Additional Information:
Your DSL Connection Rate :3.26 Mbps(DOWN-STREAM), 448 Kbps(UP-STREAM)
IP Profile for your line is - 2.5 Mbps

Your service was found to be performing poorly. Please raise a fault with your service provider, stating that the BT Performance Tester tool indicates poor service throughput performance after the third test.
Line Speed
Estimated line speed:
    1.0Mb (Accurate to within +/- 1Mbit) - Checked on 2012-01-27 20:19:58
Current line speed:
    3 Mb

[#2]

Yeah, I've been getting much the same thing the last few days.
Just done BT & Thinkbroadband tests - both coming up with a download speed of < 1MB on a connection which is between 4.5 and 6 MB with a usable SNR even in the evenings.
Tried gateway hopping and rebooting the router - nothing doing.
I suppose the usual line about the network being "out of balance" will be trotted out, but something's not right. 

[#3]

HI guys,
it does seem that there's some issue afoot. I'd recommend keeping an eye on this thread for updates
Jojo