Curly bay leaves - why?

jackie.lyall

I have four bay trees which were until the last few days looking great with lots of new green leaves forming.   However I noticed at the weekend the new leaves were starting to curl inwards.  I thought they were maybe just dry so gave the trees a good feed and water.  It made no difference. I can't see any pests on the leaves themselves. Can anyone help with what might be the problem?