keyless entry boot lock not working

[Brigante]

I have a 58 plate mondeo with keyless entry. The little button on the tailgate used to lock the tailgate works very intermittently. A lot of times it will not work at all, at best it will only single lock, no matter how many times I double press the button I will only get a single lock out of it. I will end up walking around to one of the front doors instead and double pressing the button on the handle to lock the car without issue.

 

This is very frustrating if I'd stood at the back of the car with a load of shopping bags in hand wanting to lock the car and I've got to shuffle down the side of the car to the driver door to lock the car.

 

Can anyone offer up some advise on tackling this issue to regain control of the tailgate lock?