I think this is a leuchistic Northern Wheatear - although I am open to any other suggestions !
It was occasionally associating briefly with two normal juvenile Northern Wheatears at the base of the sand dunes at the back of the beach at Turnberry Bay.
It had the characteristic upright stance of a wheatear and had a similar short fluttering flight.
The other Northern Wheatears seemed to tolerate it but the Rock Pipits did not like it at all and would drive it away.