Tony comments that the internet is very slow. I try to remember how to log into our router to run diagnostics, but while waiting, check my email and find an email from PlusNet saying "you may have noticed your internet connection is slow, this is because you have exceeded your monthly usage allowance". Our allowance is 8Gb/month and we usually average rather under that.

I log in to the online customer service, discover that the vast majority of the downloaded traffic is peer-to-peer, switch us to pay-as-you-go for additional usage allowance for the rest of the month (which will restore our usual ADSL Max speed of ~4Mbps), and go to have a firm word with my brother. He will pay the additional costs incurred while he stays with us, and I have drawn his attention to the "Free Usage" period of midnight-8am.

Within a few minutes we are back up to normal connection speeds. What could have been a deeply tedious situation is now resolved with minimal hassle. Hurrah to furrfu for recommending PlusNet to us.