slow speed since 26/03/14

[#1]

I have been enjoying speeds of over 11 Mbps for months with no issues at all.  Since the evening of 26/03/14 my connection drops and reconnects at odd times and my download speed has dropped to around 3 Mbps to 3.9 Mbps.  Nothing has altered at my end.  I have tried using your broadband troubleshooter, but it seems that if I don't buy an alternative router then I am being threatened with having to pay for BT to look at my problem.  Some help would be appreciated as I need this Internet access for work.
Thanks in anticipation,
David

[#2]

Hi David,
I've just had a look over your line and can see an entry:
26-03-2014 20:34:17 - 6006K
Looks as though something caused your speeds to dip on Wednesday night. Your speeds to your router have since returned. I've sorted your speed profile out on our systems. You may just need to restart the router for the speeds to return.
If you have any further problems with your connection, I would advise completing the Fault Checker at http://faults.plus.net so we can get this investigated in more detail for you.

[#3]

Many thanks Chris.  Everything seems to be back to normal this evening.
Cheers
David