What type of Diver is this?

Firstly apologies for a poor picture, was getting dark and was at full zoom...

I initially thought this must be a black throated Diver in it's winter coat but consulting the books there is no reference to the reference to the red line from this birds eye to beak. The line seems a bit too distinctive for it to be ignored by fieldbooks?

Anybody got an feelings on this? is it something obvious?

This was spotted near Shiplake, Oxon if that helps.

Thanks for any help

Mark

Learning more and more as the weeks go by