Sorry don't have photos but reporting for the interest of any fellow feathered-biped enthusiasts.
It made a sudden dash from a neighbour's dense bay tree (which is pretty massive for a bay tree, unless I've been misinformed about what it is) to another neighbour's equally massive conifer.
I had noticed a parakeet come in to settle on the same conifer a few minutes earlier - I've been able to attract them to my bird feeder of late and I figured it was waiting for me to vacate the garden.
The parakeet and a wood pigeon both fled for their lives at their respective top speeds.
It must have been going for the wood pigeon because parakeets are nowhere as slow and lumbering.
About ten minutes later the noise I was making in the garden spooked the sparrowhawk and it made off. I hadn't realised it was still in the tree. When it flew off it was carrying something small, which I'm guessing might have been a wood pigeon chick. Which in turn might imply it had been hanging around at the wood pigeon's nest devouring the rest.
About half an hour later the tits and sparrows were back at the feeder and shortly thereafter the parakeet came back too, so hope that qualifies as a happy ending.
I had one in the garden of my old flat in Stroud Green a few years ago, which also killed a pigeon. Always good to hear wildlife sightings in the area, thanks for sharing.
Avove Harrow we often have Buzzards & Red Kites. I have often seen the pigeons etc go into panic & have seen them chased by either sparrowhawk or peregrine? Just read up on the peregrine, they are able to kill buzzards and like eating ring neck paraqueets too ! In the case of Harrow, these green birds have now totally overrun the area, so we need more predators. send them over.