http://www.karoo.co.uk/broadband/faqs.asp#over .......a lot of trees, that's why they're charging a £1 for paper bills.
What happens if I go over my usage allowance? How much will it be if I go over my usage allowance?Your first usage period may cover more than 30 days. So to help get you settled onto your new broadband package – additional usages charges during this time is unlimited and completely free. Subsequent months will be charged accordingly. If you go over your usage allowance, you will be charged £2 per GB or part thereof if you're using Karoo Lite, or £1 per GB or part thereof if you're using Karoo Mid or Karoo Pro. The payment for additional usage will be added to your next monthly payment, which will be taken on or around 29th of the month. We will notify you in writing of the changed bill.
i.e...If you use 78.01gb you will be charged an extra £4 on your next months bill.