Buy a power/current tester from any DIY store.
Connect the site lead to mains and van run test through the wholed circuit up to the MCB in van see if there is a break in cable or duff plug on site lead. If the leads up to the mcb in van test ok ensure main switch on mcb is on check the 13amp sockets and mains light if you have them in the van if ok it could be the leasure battery is knackered and there is nothing wrong with the onboard charger and nothing to do with mains. hope it helps.
Bob
August 2009