Lawn Problem.

What do you think my problem is?
These light patches have appeared in my lawn over the last few weeks and appear to be getting bigger.

 

Doesn't look like moss and the yellowing is typical of leatherjackets (daddy long legs larvae) or chafer grubs.

There are nematode solutions available as an alternative to pesticides but they may kill the worms too, of which most types help your lawn grow.

 

Looks like the effects of animal wee to me, but your lawn looks good for the time of year. I regularly visit on of the rhs showcase gardens (harlow carr) and their lawns are looking worse than yours at the moment.