A warning on screen said "key battery low"' I replaced the battery with new ones, still the same fault notice appeared. I have bought a further set to be certain the battery was not at fault but the same warning appears.
I have searched related post but I can't see that anyone has had a similar problem.
Please help!

What brand batteries are you using ? I had the same prob. Got a battery from local motor factors, fitted it and still got same message.Then fitted a Duracell battery and worked fine

Hi Brooksy
Poundland specials- perhaps go get what you pay for!

Will try Duracell this weekend.
Cheers Phil.

Put new energiser batteries today- did the trick. Working fine now.
Thanks Phil.

How are you guys swapping the batteries so easily? I only was able to change mine because I transplanted the guts to a new plastic FOB. I had to desolder the old battery and solder in a new one. Or does the UK have different FOBs than we do in the states?

Sounds like you have a different fob to UK spec. To replace the batteries take less than a minute.Plenty of how to videos to show you how they are fitted.
Good luck!

Once you replace the battery (2011 model, 2032 battery), you need to lock and unlock the car using the remote to clear the error message. Check YouTube for how to open up the remote 2011 Vogue TDV8 4.4
1992 Mazda Mx5

For reference, on my 2009 RR, I had to do something similar to these videos:

To get to the circuit board, it takes a lot of plastic wrangling:
https://www.youtube.com/watch?v=RM6SzJ3e4uE

Once out, I had to desolder the battery and solder in a new one:
https://www.youtube.com/watch?v=0YgpDWx-uH4

No, this is not me! I did have to mangle the old FOB in a similar way to get to the battery and PCB, but once inside I didn't abuse the thing like this guy does.

Edit: Typo.