Not the usual IT support problem - TomTom Home (v2.9) wouldn't connect to the shop using Windows 10, so I couldn't actually pay for the maps upgrade. This is for a Mazda NB1 satnav fitted to a Mazda CX-5. That started me looking at alternatives. The same version on Windows 7 was ok, connecting to the shop and quoting £59.95 for 12mo updates (ouch!)
I tried looking at the TomTom website to directly purchase maps. There was a Western Europe map for £44.95 on offer. Part way down the screen it says type the first two letters for your TomTom model - thats DP in the case of the Mazda NB1 - however its not compatible. Sigh!
In the end, I worked out that you need the full European map for this model. This was listed at £59.95 (reduced from £69.95) plus there was an offer for 18 months of updates, instead of 12mo. I looked on vouchercodes and there was also a new customer code of WELCOME15_UK giving another £8 discount.
Then click on Update My device and the new European map will appear on the list to download to the memory card. One last issue, its too big to fit, so I ended up selecting EU Zone 8 which seemed to include UK, France, Spain and Germany (that's this summer's road trip covered).
So £52 for full European map with 18mo updates seems a much better deal than the one offered on the automatic download via TomTom Home. Sounds like there are 30% codes available too, depending upon the time of the year.