Tomato plant leaf problem

We have tomato plants in the greenhouse in grow bags. All of them have leaves that are shrivelled (closed up?). My son maintains that it is due to over feeding but I have only fed once and they had closed up leaves before that. He thinks it is the gro bags themselves (with the wrong fertiliser in?). We had no problems at all last year with a mini greenhouse. This one is a 10 x 6 with two auto opening roof windows. I have uploaded a pic of one plant. Any help would be appreciated.

Thanks

Brian

 

Its quite normal, but might be down to very bright sunlight under glass.

 

When I used to grow them (under glass) it happened to me a couple of times. As Pete and John have said, it’s nothing to worry about.

 

Thanks to you all. That's a relief.