No interactions present.
You often find in places with lots of food but few nesting places that birds lay their eggs in other birds nests. This could be what is happening here. I found a ducks nest in a Southport park that had over 40 eggs in it, including goose eggs.
I was considering this as both birds were settling the eggs. Couldn't see exactly how many were in there, but Martin Mere does have plenty of nest sites. Worth considering though.
Just go out there and do it!!!
Lat/Lng: 53.622588427316, -2.8653287887573
OS grid ref: SD428143