Diesel Midi won't start?

I have a 1989 Bedford Midi with a 2.2 Isuzu engine. Had a new cam belt (pro fit) 1000 miles ago. Pulled onto drive and turned it off. Went to start it 3 hours later, engine whizzing over but won't start. Have checked it's getting diesel and has compression. Checked starter relays and resistors. Replaced fuel filter/water trap. Is it back to the garage? Could the belt have jumped a tooth and the timing be out?