2005 Vauxhall combo 1.7 cdti will start ok on a flat level , when parked on my drive facing uphill it will start and then stall , then takes about 6 goes to start again . I think it has something to do with fuel running back to tank as its fine if facing downhill or on flat , is there any kind of return valve in the fuel lines which are not working correctly ? .

SOURCE: Focus Diesel 1.8 tddi difficult to start when facing uphill

There is leak in the fuel system and air is coming in somwhere. Maybe the hoses with the injectors are leak.

SOURCE: Hilux fuel return

I think the in-tank fuel screen(the "sock") has come off.This screen allows the pump to **** up the last bit of fuel in the tank.To verify,see if it does it with a full tank.You can either carry a 5 gallon gas can,or just fill it up all the way and try parking in a known uphill spot that causes the condition.If this isn't it,then youv'e got me as to what it is.

SOURCE: 2003 cummins diesel stalls when fuel level between 1/4 and 1/2.

Check that the tank is not under vacuum caused by a blocked vent.