Finally!
Downloaded the UK maps to my memory stick. Printed out the instructions(which were a touch confusing). Extracted the files to my USB stick . Got through the first bit. The last 6 digits of the VIN were already displayed, followed the instructions, entered the code selected the map, selected "update" and waited. Maps started updating but error message "Data incomplete or corrupted". Tried several times without success.
Found and formatted a different memory stick (although the first one was brand new and formatted).
Downloaded the updated maps again, extracted to the USB and shoved it into the port in the car. Needed several tries, as "update" was greyed out . Finally managed to get the code loaded and the update selected as it suddenly became available on the third try. Waited with baited breath and fingers crossed while the slider crept along. Just over 30 minutes later, I got the welcome message that map updates were complete!.
Full postcode search is working fine.
I'm now thinking that Marc's Firmware download instructions would have worked fine, and my brand new USB 32Gb Scandisk Cruzer Force memory stick was the problem with uploading to the car. It cost me £11 to buy a CD and £40 for the garage to upload the firmware from it. Hindsight is a wonderful thing, although I did try the CD method myself without success. I'll be using the sat nav this afternoon, on a short trip that I've done before so we I will see how it performs. It has had a tendency to get lost on newer roads and junctions and I'm looking forward to a better experience.

Rick.
2013 Citroen DS 5 D/Sport
2007 Renault Clio Campus sport. 1.2l
Sometimes the change doesn't work.