Saw this bird in the garden last August in Scotland, it had just devoured one of the small garden birds and was being harrassed by two magpies who seemed to object to its presence. Seemed to be a goshawk as far as I could tell looking at pictures of the sort of raptors found around here but i'm no expert. The pictures aren't great as they had to be enlarged a lot and two were taken through binoculars.
Gos would be HUGE compared to those Magpies: Magpie is 40-50 cm long, Gos is 50-65 cm long with a proportionally much shorter tail. Or put another way, a male Gos weighs as much as 4 Magpies, and a female Gos weighs 8 Magpies.
Thanks, It eventually flew off but didn't seem too bothered by the magpies, I'd guess crows would be more of a threat to the sparrowhawk. I see lots of big prey birds high above out on walks around here but they're too high to make an ID possible, like here: