xpd: How many devices are connected ? Turn them all off/disconnect except your own and see if the issue remains... if it comes right, its one of those other devices.

If you only have one device connected and its doing it, I'd suspect youve got some malware or similar running - install a bandwidth meter on your system and check what it shows is going out.

http://www.softperfect.com/products/networx/   is great

Found the problem, thanks. My mum was uploading all her pictures and documents to OneDrive.

how dear she upload pictures and slow the interwebs!