What is the likely fault on my X Type Jag(05)?

Car has driven perfectly for 2 years. Drove into New Forest on dusty bumpy track for 2 miles, parked up on uphill slope and went to wedding. Returned after 4 hours and car would not start/fire. AA unable to fix, now garage says fuel (diesel) supply is intermittent and rocker shaft has worked loose and want to refer the job to a diesel specialist. Any ideas about the true fault?