I have found out today the problem has been my energy monitor, that has a transmitter attached to my electricity meter, it had a fault which meant it was transmitting continuously. Have thrown it away and now the remotes work perfectly. They must be on a similar frequency.

Had a problem locking and unlocking my Disco, had to press the buttons probably 20 times right up close to the car to get a response. Changed the batteries in the fobs, still the same. Turns out it is my home Internet hub that interferes with it! Move the car away from the house and both keys...