Update
Mark tried to check out the ECU with Tech II but as at the time I had no speedo and the two dreaded orange lights (TC and ABS) not surprisingly Tech II could not communicate with it. Conclusion ECU knackered (dbug gets the prize for the correct diagnosis when I first posted symptoms six weeks ago). I briefly flirted with the idea of a used ECU but when the cost of reprogramming is taken into account I decided a refurb of my own unit was probably the best option and following Marks advice checked out these people who are on the doorstep for me
http://ecu-testing.com/. I managed to get the ECU repaired for £100 all in (collected) as they had an offer on ebay at this price rather than £100 + VAT on the website. (If you ring up and tell them you have seen them on ebay at this price you will probably get it for £100, worth a punt) They turned the repair around in less than 24 hours and provided a two year warranty. When I picked it up I asked what caused the failure and was told it was a break in one of the fine wires running to the ECU chip. Refitted the ECU this morning, easier than removal now I know what I am doing (remove battery, top hose and power steering reservoir hose to pump connection and use a flexible shaft Torx bit holder fitted to driver. Also helps if you have small hands and huge patience) I held the screws in place in the ECU casing with a blob of household silicon sealant in each hole, leave an hour to go off then refit. Stops the screws falling out repeatedly. May be easier to put screws onto Torx bit and then then fit into holes whilst holding, but silicon sealant worked for me. First fit the flexible holder to the screws with fingers then fit the driver handle to the flexible shaft and tighten as much as you can.
Many thanks to Mark, dbug
et al for advice and helping me to a tidy saving of several hundred pounds compared to Vx price for a new ECU. Not quite so exciting now playing speed camera roulette without a speedo but at least the licence is safer.