To be honest, I think that with the virus update, your 'phones and whatever else your computer system does in the background would put you over if it was accounting iPlayer as usage. From the account you give iPlayer would account for the entirity of the discrepancy and the rest used little or no data at all which is fairly hard to swallow.
Much of the data accessed by portable devices is in the cloud which is accessed silently and without your knowledge. Do you have any automatic backups happening? Anything going to BT digital vault is not taken from your allowance, but anything from your portable devices may. You could check that by looking at the upload figure on the usage meter.
Is there a mechanism on the phones themselves to show their data usage? I'm sure there must be an app for it.
If you have a look at the iPlayer website you can see how much space a programme uses by clicking on "download options". Don't forget to look at the HD version if you've been using that.
As an illustration: The One Show uses 561MB, The Apprentice uses 1.2GB and those are for the exact duration of the programme without the filler material.
