My connection cut off about 20 minutes ago and when it reconnected I had been assigned an IP in the 81.152.*.* range whereas my IP is 80.229.*.* - I couldn't use the Internet at all with this IP so I reconnected and got my usual one back. Why did this happen?
This is usually assigned by BT if they cannot connect you to plusnets radius server (which is responsible for allocating your PlusNet IP etc) and it is not possible to surf with it as you have seen.
This does happen from time to time and often just disconnecting and reconnecting solves the problem. If it keeps happening then manually set up your PC with plusnets DNS servers and this usually cures the problem.
There can be many reasons why this happens but it is most likely an intermittent BT routing issue somewhere.