1997 LEYLAND DAF 45 150 Horsebox STARTING PROBLEM?

After being used intermittently in winter, vehicle was allowed to stand for 2 months. It started OK but wouldn't rev, stopped and wouldn't re-start.

Found no fuel being delivered, first suspected lift pump (checked, OK) and then found the push-fit fuel pipe water from separator-lift pump was loose at the separator. Re-connected, cleaned out separator, primed up but it took much cranking to start, but seemed OK when it did.

Left overnight, failed to start again. Primed through, including cracking 2 injector pipes, all OK. Finally started, again after lots of cranking, and taken for test drive. Seemed OK except for some hesitation full throttle under load in low gears.

After stoppng the engine normally, it wouldn't re-start. Primed through by cranking on the starter and occasional bubbles spurted out of bleed nipple as if air was getting in somewhere. Rechecked connector at separator = OK.

All pipe connections checked, primed again and no bubbles evident but it still wouldn't start before battery went flat!

What next?? Help!!!