Hello there.
I had a very similar problem, After three weeks at a local garage they couldn't get in started and gave up but insisted it was a fuel problem. They didn't have the fuel pressure test kit that RJ mentioned earlier, so of it went to a BOSCH specialist, tested it and it passed. Yet still wouldn't start.
In the end it turned out to be the old factory fitted alarm that i have never used since owning the car. The alarm was preventing the engine starting by randomly shuting off the ignition, or fuel or both. They took out the alarm, repaired some frail looking wires and connections to the E.C.U and HEY PRESTO! I cost a few Quid to fix, but that was due to labour. They also put in a Recon E.C.U at £100 because some of the voltages coming out of the old one were iffy.
Good luck.