Bird of prey ID reguest

Hello. I'm a keen novice photographer who has a thing for wild birds of prey.

On my way to work this morning I spotted a raptor perched on the hedge on the other side of the road - one that I didn't recognise. Frustratingly I couldn't stop to take a photo!

It appeared to be of large female buzzard size and a similar shape, but the head, neck and under the wings (from what I could see) were white. Not speckelled or light brown, but white.

I am familiar with what red kites, common buzzards, honey buzzards, ospreys, goshawks, sparrowhawks, kestrels and most common British raptors look like and have discounted them.

My Googling has returned a couple of images that do look similar: a Mississippi Kite - which I have also discounted because the bird I saw didn't have the black around the eyes, and the White Bellied Sea Eagle. The latter is very similar, if not the same colouring. I am aware that we are a ways inland and these magnificent creatures are normally found in the southern hemisphere, but it's the closest match I have.

I can't be certain on the size - these sea eagles are rather large, so that's the main thing that's stopping me from saying that this is what I saw with any certainty, but, I find that you can't always appreciate a birds size until they take flight.

Can anyone think of what else it could have been? The location was on the A5 near Little Brickhill at around 10:30 in the morning. Not too far from Woburn - one of my thoughts were that it was a captive bird that absconded from a display, but I don't think they do displays at Woburn Safari Park.

Any suggestions would be welcome.