An osprey!

Sitting on our deck in the late afternoon I looked up and saw a large gull circling. It began to ride the thermals and I got the binoculars as I thought this was a bit "un-gull-like". The bird was larger than I had first realised and had a greyish white underside with black tips on its wings. I watched it until it got so high that I couldn't see it clearly even with full zoom on the binoculars. Looking in my bird book it could only have been an osprey, and this was confirmed by the RSPB page

Seen in flight from below the osprey has white or slightly mottled underparts. The long wings are angled, bending at the 'wrist' which has a black patch contrasting with the white wing linings, and at a distance it could be mistaken for a large gull. This spectacular fish-eating bird of prey is an Amber List species because of its historical decline (due to persecution), and low breeding numbers.

I wonder if this was one of the Bassenthwaite ospreys? http://www.ospreywatch.co.uk/index.htm