Any advice for '3' mobile broadband connection problem?

My normally reliable ‘3’ mobile broadband connection has started failing about every 5 minutes. This occurs even if the signal strength is indicated as being at maximum. When the connection fails, I can successfully reconnect, but after another 5 minutes or so the connection fails again, and so on ad infinitum. I am using the broadband dongle in the same place that I normally use it. Furthermore, I have made no recent changes to my system or installed / uninstalled any programs, so no obvious culprits spring to mind. I am running Windows XP with Internet Explorer 8. Any advice on solving this irritating problem would be greatly appreciated.