Favoritos de aveid

A challenging ID- would appreciate any ideas though I know the photo is poor.

This raptor flew across the river into the wetland, harried all the way by several seagulls. It stayed fairly low, treetop height- about 3-4m off the ground (although that could simply be due the seagulls harrying it). It was at least 2-3 times bigger than the gulls.

Underwing/underbelly was distinctly uniform pale whitish/grey with some dark colour only along the margins of the underwing and tail.

Osprey are known in the area, but I thought it looked a bit different as the undercarriage colour was solid rather than mottled. Could be wrong.