Thanks for the reply guys, don't think it's the battery because followed a test from the haynes manual.
1) turn on main beam, watch for 20 sec to see if lights dim (they don't) this is to check battery.
2) leave main beam on and turn ignition key, if lights dim it means power is getting to starter motor and this means there could be a problem with the starter motor (they don't dim)
it also says that if the lights stay bright and no clicking sound from the solenoid this is a fault in the circuit or solenoid (but ours clicks and lights don't dim)
This makes me think there must be a problem with the actual starter motor.
Bumped van started ok ran good but once turn off same problem again, so will take starter motor off tomorrow and get tested.
Will post any updates thanks
alut: