After nearly 5 months of problems with BT Broadband, it took only a few seconds for someone to check and find that I had been capped.
When I enquired about what were the used measures, they were happy to advise that they did not publish them! and would not tell me what they were - when I pressed the harder they advised 'off the record' that there was a cap set at around (yes around) 40GB where they would reduce the speeds during peak time only (they suggested this to be between 6pm and midnight) but if the usage crept up to around 100GB (yes around again) they would restrict speeds 24 x 7 - both caps allegedly in place for a month. However they were not able to tell me what around exactly meant and would confirm none of it in writing. Neither could they advise where I could find the written 'policy'
Therefore having been capped on a monthly usage (number provided by BT) of around 40GB last month, I would have expected no evidence of the restriction past the midnight hour - yet it was there, so I am not sure what time zone they are working on.
When I pointed out that without the information it was impossible to make an informed decision as to which provider the customers could choose, they also were keen to push back and quote that Ofcom agree that they do not have to publish it!
I should also add that they did give me a refund for the last few months, not due to the usage issues but because they did not check if the 'capping' had been applied - However, the promise of apology and confirmation in writing has still not been forthcoming.
This is my own experience as recent as this past 10 days so I do hope that you find this useful.