OK I've managed to get a pretty stable connection for the last couple of weeks using this driver version:
15.8.0.5
There is a newer version but that messed things up so I went back to 15.8.0.5. I also tried uninstalling the Intel Proset software but that seemed to cause problems so I reinstalled it. I found the software and drivers here:
http://www.intel.com/support/wireless/wtech/proset-ws/sb/CS-034041.htm
It's labelled as 15.8.0 but when I install it, the drivers show up as 15.8.0.5
It looks like we're almost at 50 pages worth of threads for this incredible fail by Intel. I'm tempted to send this to the technical reporter at the BBC, it might make for a rather amusing news item!
Intel - do you actually have a fix yet or should we go to the press?!