Just thought I would update on my thread from last week, as I've now achieved a working solution from the information received, so, many thanks to:
The Boy,
Andy H,
Entwood and
Vega, for all your input.
I found a "YP" module with two fobs on eBay for £15.00 which I thought would be worth experimenting with. Although not exactly the best match, YP should be a compatible replacement for my ES. As it had come from a saloon it had 3-button fobs rather than the 2-button ones I needed for the estate, and it had no pass code number.
So I changed the modules over and tried the key in the door lock first. It worked, and set the alarm, so at least it proved that the fault had been in the old module. So then I tried the fobs and although both extremely beaten-up and manky, the first one worked fully, and the second one would unlock, but not lock (micro switch?), Swapped my key blade onto the fully working fob, so now I seem to have a working solution.
As I have long term plans for the car, I would really like to find a module with 2-button fobs and a pass code, so that I can get new keys programmed in the future if needed. I thought I had found just that in the 3.2 MV6 which Joff is breaking, but when the module came out it was an "LT", but thanks, any way, to Joff for his help.
If anyone has any snippets of info on which years/models use ES or YP modules, it would be very much appreciated. Thanks again for everyone's help.