Squawking at sunrise

Hi all, 

I've recently gotten into bird watching and loving it. First post on here for some help please.

I was woken up a week ago by a raucous of squawking. Lots and lots of these birds had arrived in the field behind my house. They cluster in groups of around 10 and utter cries similar to seagulls but higher pitch. Any tips on what they are?

Thanks!

Bryn