Likely the module in the wheel arch is gone , they get water Damaged . You can swap the good one from the other light to see if the fault goes. If so you know that’s the issue . I got a used bmw one off eBay £150 you can get 3rd party for about £50

 

Thanks. Are they easy to get to then or is it a garage job?

 

Do check to see if the bulb has or hasn't gone - similar, switch the working one over..
Youtube may have someone done it and video'd it

 

Easy enough to get to. Turn steering wheel full lock away from you to get more space and jack up the front of that side . 2 screws hold the access panel closed . Once that’s open you can see the module in front of you . Get a mini t20 driver that’s shaped like an Allan key as there is hardly any room . Module held in by 2x torx20.
Once the screws are out you have to wiggle the module out .need to be quite firm but it does come up . Installation is the reverse .2nd hand shouldn’t need programming in and 3rd party off eBay etc will say plug and play if that’s the case . Trying swapping the module from the working set of lights to confirm that is the fault

 

Thanks for that.