Speed troubles

[#1]

Hi,
New plusnet customer, have received great speeds over 13mb mark during the first week or so of the connection. However recently that speed has dropped to well below 8mb, this morning bt speed tester put my speed at 4mb. My ip profile is set at 14mb, so I was wondering why I have this disparity in speed?
1st bt test:  Download speedachieved during the test was - 7642 Kbps
For your connection, the acceptable range of speedsis 4000-21000 Kbps.
IP Profile for your line is - 14000 Kbps
The throughput of Best Efforts (BE) classes achieved during the test is - 9.14:4.36:86.5 (SBE:NBE:PBE)
These figures represent the ratio while sententiously passing Sub BE, Normal BE and Priority BE marked traffic.
2nd bt test: Download speedachieved during the test was - 3999 Kbps
For your connection, the acceptable range of speedsis 4000-21000 Kbps.
IP Profile for your line is - 14000 Kbps
The throughput of Best Efforts (BE) classes achieved during the test is - 3.58:34.39:62.03 (SBE:NBE:PBE)
These figures represent the ratio while sententiously passing Sub BE, Normal BE and Priority BE marked traffic.
Any help greatly appreciated!
Thanks
James

[#2]

Hi portercam,
Your profile on our side and on BTs is showing at 14000 as well, so I can't see any particular reason for the change. Is there only the one computer on your network, and was the computer running the speed test doing anything else online at the time (windows updates perhaps, or possibly antivirus?)