The car currently fails the headlight testing.
At the moment my only option seems to be a complete replacement of both headlight units at £1000+ each.
Has it been explained to you by the tester why the car currently fails the headlight testing? The information I received from BMW GB states that "the xenon technology incorporated into your vehicle's headlight system uses flat beam technology. To make sure that vehicles driving towards you or ahead of you are not dazzled by this stronger light, BMW xenon headlights incorporate a projection lens which directs the light beam straight to the road."
In other words the headlights are now the same for both LHD and RHD cars. Given that if your car is actually failing some test presumably there is something else wrong? Or is it the case that your tester has not actually tested anything but simply 'assumes' that it will fail because he can not find any manual adjustment?