More information... I had Mydrive Connect running and the device connected to my computer while doing something else. I bumped the device and it began to connect but failed to complete. I think my problem might be down to the (non genuine) cable not being a good fit in the TomTom.
TomTom of course don't sell cables in New Zealand and will not post to here from the UK so I have bought a GO 1005 (on which the Alfa unit is based) for sale on our local version of eBay, complete with a genuine cable, for about the cost of a new cable. As well as the cable it will be a good test mule for installing new software and updating the maps. I'll report back when it arrives and I have had a chance to do some more tests.