Both were structurally very similar to Glaucous Gulls - large size, shortish primary projection and large bi-coloured bills. The first one, a first-winter, was a large gull with pale buff upperparts and greyish brown primaries. It had a full greyey brown tail band, which is not that common, but certainly not unprecedented for this hybrid type. The other was a second-winter. When I spotted it it was facing head on and I thought it was a Glaucous, but as it turned sideways on I could see its primaries were not right - too dark.