Plusnet ADSL latentcy/contention issue
 

I currently have a plusnet ADSL connection via a Market 1/BT wholesale exchange.

Over the last few days, my pings to google.com have gone from 20-40ms or so all the way up to 1000ms or more. The odd thing is that the speed is about 3-5mbit (its usually 6-6.5). The sync speed and line stats are also still the same.

Its worst in the evenings, in the mornings its pretty much ok.

I've raised the problem with plusnet, but are there any other investigations I can carry out from my end?