Where we live, during summer, the clay underlying our lawns produced
cracks

ours also cracks (not a badly though ). Is there any point in trying to
fill the cracks with sharp sand/compost? I've often wondered if this would
do any good or if it would just make it more compacted in winter - any
suggestions anyone please?

--
Hayley
(gardening on well drained, alkaline clay in Somerset)