Hi Tinsel :wave: I'm glad you asked that question because only one week ago, I was stood on my backdoor step when a kestrel (I think), swooped out of nowhere and pinned a starling to the ground. I stood there, stunned, before the kestrel eventually flew off with its catch. The rabbits were out in the garden at the time and I have to say, they didn't take the slightest bit of notice. This did surprise me because they usually take flight when a helicopter or light aircraft flies overhead and are very wary of anything large in the sky.
Like others, I thought a Buzzard would pose a threat and they are Britain's most common bird of prey. Some owl's could be a threat but are generally more likely to be hunting at dusk when our bunnies are safely tucked away for the night. I do supervise my bunnies in the garden but, to be honest, with the speed at which the kestrel struck, I don't think you'd stand a chance at intervening if a buzzard did attempt to take a pet bun. I had no idea it was there and it had struck and was gone before my brain re-engaged and I could think what to do.
It's one of those times when you've got to weigh up quality of life over risk. And it is a fairly small risk when all said and done. I think foxes pose a greater threat.