Hi
These are much darker than the local breeding birds and are very likely to be ‘northern’ birds migrating. We do get the fully black faced birds passing through our area, usually in May. Your birds in the photo may not be in full breeding plumage yet or they may be intermediate forms.

The extent of the black varies with latitude and with altitude. I have seen fully black faced northern types breeding in the Cairngorm mountains. Some less black forms breed in Iceland.

I think we can be sure yours are not local. Nice photo.