Aubergine's leaves dying off

Planted in my pollytunnel, grown to about 2ft high, have flowers and in the last week leaves started to wilt and then go brown, no fruit yet but the plants look like they are dying.
Grown in a bed (about ba foot deep on a bed of soil) filled with spent compost from last years tomato bags, some 1yr old horse manure and also mixed some chicken manure pellets.
Also growing in the tunnel are sweet pepers (next to them), tomatoes and cucumbers, watered four or five times a week, seemed healthy until now.
Same thing happened last year about this stage.
Any help would be greatfully received

I don't know why but I see this with my plants too. These are grown out doors though. I am still getting some lovely big aubergines from them though. We have had some really hot dry weather for the last 6 weeks and I think they just lose the odd leaf now and again. The do like hot weather so I am not doubting it is watering is a possibility that is the problem but you say you are watering regularly?? Here is a photo taken two minutes ago of my plants you can see some leaf browning which has been happening since early on... but still some really nice fruit?

Thank you for the replies, I think your right about the heat in the tunnel, next year I shall try them outside.
The tunnel has a door at each end which has netting on the upperhalf but even then I have seen max temps at the 45 oC level.

I would honestly keep them in the tunnel 45C is by no means a high temperature for these plants. I grow them here where we get shade temperatures of 37 and up in the summer is not at all unusual go out into the sun and it is very much hotter. I really think it would be a mistake to grow them outside in the UK if you really want a good return from your plants...especially when you can grow them in a nice warm tunnel. I know people down here who grow their tomatoes, peppers and Aubergines tunnels... last year we had shade temperatures of 44C  As long as you water them properly they should be OK. Whereas growing them outside leaves them open to temperatures they will not like at all and significantly shorten your growing season

A happy update
Gave them some more water and a liquid feed and hey presto got about six fruits now, growing well as far as I can see
Happy days