My campervan won't start

Are you allowing time for glowplugs to warm up? What's showing on the instrument panel? 

Yes but they only stay on for a few seconds

I'm no mechanic but when I had a boat if the engine did not start it was usually a fuel problem.  Are you able to check if fuel is getting to the injectors?  Could be blocked fuel filters or the dreaded water  (condensation) in the fuel.  Are you in the AA or equivalent, might be time to call them

I've just googled 'my diesel engine won't start'.  Plenty of tips which mainly point to fuel problem.  Good luck.

When you first switch on, can you hear the usual pump and other whirring noises? When you say 'stay on for a few seconds' do you mean the red glowplug symbol or all the other oil pressure, battery, et cetera lights as well? They should stay on until the engine is up and running. You may have a bad connection problem eg earthing. Is your immobilizer responding? Try another key.

I'm not an expert, but I can imagine how frustrating it must be. Your battery obviously isn't flat.

Got plenty of fuel?

Is your LV on a slope ,has the fuel still to be pumped to the injectors?

As stated above, many starting problems where the engine is turning over on diesels are either injector failure or fuel pump. You can listen to determine whether the fuel pump is working and there are ways to start the engine if the injector fails, you can squirt Easystart (I think it’s called) into the manifold but you need to know how to do it. It’s a job for the AA or a mechanic. 

Thanks for your help will try your suggestions tomorrow 

Don't use Easystart. It's crack cocaine for engines. Once hooked there always need it.

Yes, I should have mentioned that if an injector spring fails you can squirt it in the manifold to start the engine to get you to a garage. Once you switch off you would have to use it again to restart.

I broke down at Dover and the AA got me started. Unfortunately we then had to drive 100 miles back home with the caravan on the back, unhitch, drive to the garage; all whilst keeping the engine going. The upside was that they fixed it the same afternoon and we went back to Dover next day and continued our trip (several hundred pounds the lighter).