Following on from The Colonels tips, are there any strainers or filters before the fuel pump that could be blocked?
Definitely sounds like the fuel filter canister to me, just checked my W/s Manual and it's just forward of the offside front suspension turret under the bonnet (see item 3 in attached) , Dedra and Thema often had this problem as they are far more difficult to get at than a Delta, which suggests ignorance or neglect of proper servicing.
Brian
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