Car unlocking it's self If the keys are anywhere near the car even when the keys are in the house.
I can only stop this happening by putting the keys in a metal tin with the lid on.
Any thoughts as to how I can stop this happening

 

Sounds like the transmitter is continuously transmitting the unlock signal. Snap open your fob as if you were going to replace the battery and clean the contacts for the unlock button.

. . . and welcome to the forum!