FTTC Download speeds

[#1]

FTTC installed on 29th March and profile updated the following day by Plusnet. However I am confused by the speed readings I am seeing. The BT speedchecker shows 25Mb download and 8Mb upload, but every other speedchecker I have tried shows 3 to 9 Mb download and 6 to 7 Mb upload.  The upload speeds seem consistent but the download speed often varies greatly from one test to the next, even from the same speedchecker, usually being around 6Mb. The connection also struggles to handle HD iPlayer much of the time. I have carried out the tests with my pc connected directly to the modem to remove any potential local networking issues. This situation has persisted all weekend.  Can anyone suggest what is happening here ?
Thanks
Ian

[#2]

What is the plusnet profile set too? If it's not 20Mb or 37Mb then Plusnet have not set the correct profile for fibre. Also, once set to either of the 2 values it should never change (except once from 20Mb to 37Mb if you had a 20Mb profile set).

[#3]

Profile is showing as 37Mb. via https://portal.plus.net/my.html?action=stable_rate

[#4]

I've had issues with the 2 non-Bt speedtests in the past.
The one that seems to work reliably for me is http://www.thinkbroadband.com/speedtest.html

[#5]

Just tried that one now and is shows 2.7Mb down and 4.3 Mb up

[#6]

If it is still the same tomorrow (which will rule out local contention - yes it does happen on FTTC) then you will need to raise a fault and get it investigated. https://portal.plus.net/apps/kbdfaults

[#7]

ok, thanks for the advice.