Having contacted Sony, they collected the tablet, took it away to France, replaced some components and returned it.
Experience to date is that this had not resolved the issue.
Maybe it an unreasonable expectation on my part but I would not expect the 3g functionality to freeze requiring me to turn the tablet off and on to reset.
If this is to be expected using 3g on the go please let me know!
If anyone knows a simple way of reseting the GSM functionality I would be interesed to hear. Wireless mode on then off doesn't do it. Unticking and ticking the data functionality in the wireless settings doesnt do it. Combinations of the above don't work either.
I have only been using 02 so I will try Vodaphone next week ( not that I believe this to be a carrier issue ).