Although I see them to a greater or lesser extent, most of the year, There are certain fields around here that have flocks of 100+ But (Normally) in the spring.
Maybe its a good nesting area? or possibly returning migrants?, although MK is about 100 miles from the south coast as the bird fly's.
TBH I've never really thought about it until now..
I believe they are mainly migratory Chris, and move south to France / Spain to over-winter, then return to the UK to breed in the spring. The problem is they are ground-nesting and subject to predation so breeding has become problematic for them. You're lucky to see large flocks (one of the benefits of being in MK ).