Helicopters over Trumpington

It's almost 8pm and I'm hearing a lot of helicopter noise over Trumpington. Every once in a while I'd put it down to the air ambulance but that usually zooms into Addenbrookes and lands. This has been several times and has been lingering overhead. Anyone got any ideas?

I feel like I've also heard a lot of distant explosions today. Have the fireworks lot been testing again?