Unfortunately it looks like Zebabdee is right. I covered the hole tonight and had a very close look.
It looks like it is over a wooden support. I got my damp detector and had a very good poke first prod was OK second wasn't I don't think in the past I have pressed hard enough to get through the lining it went off the scale

Testing around the luton it looks like the damp goes along the whole front and in to the passenger side it seems to be OK drivers side and backwards.
I assume this is going to be a job involving pulling out the lining and seeing what needs replacing. The van is 15 years old but I 've only had it for the last 3-4 months.

I sit likely i will be able to repair this myself or will it be a specialist job.
Apart from reading everything I can find on here where can I get more info on what to do id I can DIY it or any recommendations of a pro if it needs that.
Thanks for your help.
p.s. I haven't cryed yet my gut instict didn't like the luton now i know why. Once again things are never as cheap as they first look.