24mbps download speeds but on 54mbps profile

[#1]

I've never had any problem with download speeds since I joined plusnet a number of months ago. Speeds have always been a steady 37Mbps.
Earlier this week my broadband was upgraded and now I should be able to get 54Mbps, infact, earlier this week I could.
Today however various speed test sites are reporting my speed at 24Mbps, even the BT speed test is (see below).
Is anyone else having this issue? I have the addon package that prioritised your traffic.
Download speedachieved during the test was - 24.4 Mbps
For your connection, the acceptable range of speedsis 12 Mbps-52.46 Mbps .
Additional Information:
IP Profile for your line is - 52.46 Mbps
Upload speed achieved during the test was - 8.32Mbps
Additional Information:
Upstream Rate IP profile on your line is - 20 Mbps
I've plugged directly into the router to rule out any issues with my own network.

[#2]

Have you checked here https://portal.plus.net/my.html?action=data_transfer_speed

[#3]

yeh, I'd already checked that...
Telephone number:
0191???????
Phone exchange:
PETERLEE
Estimated line speed:
59Mb (Accurate to within +/- 1Mbit) - Checked on 2012-08-20 18:30:20
Current line speed:
52.2 Mb

[#4]

Hi shaunsheppard,
Your line sync rate and profiles all look ok from my testing.  Everything is configured in the 50Mbps+ range.  If the result of 24Mbps is via ethernet, can you confirm if you have any Anti-virus, Firewall or security software running?  Does disabling this software make a difference?

[#5]

Hi Alex,
I don't have any anti-virus or other security software on this machine (or others in the house). I've tried the speed tests on multiple machines, some connected to our home network and others connected directly to the router with an ethernet cable.
It's now 22:33 and I'm still seeing speed tests results at around 20Mbps.
Not that it should make any difference, but all the machines in the house are Macs.
Should I raise a fault?

[#6]

Quote

Should I raise a fault?

I would say yes but I can see that you've already done that. Our faults team should be getting back to you ASAP, let me know if you have any further difficulties.