Can you ID this bird seen flying on the beach, please?

A large gull like bird came gliding overhead today along the shore that we could not identify.
It was flying solo. The entire underbody appeared to be white, but each wing had a distinct red patch or blotch on it. Only the underside of the bird was visible, so we don't know if it was white all over. Anyone know what kind of bird this guy is? Cheers.