We switched ISP from BT to Vodafone last week. My wife is on a Vodafone mobile phone contract and they offered her a good deal, also promising that we would get slightly faster internet than we were getting with BT.
Our connection with BT wasn't great but it was at least useable - it only occurred to me after the event that I should have done a speed test before we were disconnected for reference, but looking back over the thread, I posted a speed test result of 21.15mb/s on 3rd September 2014, although Vodafone claim BT were only giving us a maximum of 17mb/s.
Our internet is now barely useable. Upload speeds are ridiculously slow, which is a real problem because I'm now working from home full time and need to be able to share large files with my colleagues. And when I'm uploading stuff, it clogs the upstream connection to the point that I can't even send email.
After numerous calls to Vodafone, we've finally got them to stop suggesting it's a problem with our internal WiFi network (nothing has changed inside the house except swapping from the BT to the Vodafone router) and they have promised they will "investigate". If I open the router interface in my browser, it claims that we're getting ~21mb/s, though this is demonstrably a lie (according to a speed test conducted using a computer connected directly to the router by ethernet with all other data-hungry hardware in the house powered off).
There is some potential good news on the horizon though. Our problem historically is that the green cabinet we're connected to is about a mile away, and the exchange is over six miles away. They installed FTTC a few years ago but we're still on copper for that last mile. However, while out walking the dog this morning, we noticed that a brand-new green cabinet had been installed less than 200m from our house, and it appears to be connected to the line that serves our house. This is potentially very exciting news indeed.....
Now it's just a case of finding out how we can take advantage of this new fibrous goodness.........