Crank Sensor?
I know they are troublesome on the Omega, but I had the same problem on a Beetle with burning out a fuel pump relay due to a knackered crank sensor - spent hours on that bloody relay only to find it was something else.
:-?
I think Dave has probably identified the most likely cause.
The lead to the crank sensor degrades due to the heat from the exhaust manifold and disturbing it (by wrestling with the cam covers) can be the final straw.
Not all failed crank sensors bring up a code. When mine failed it didn't.
What I did notice was that with the failed sensor in place (and the engine failing to start) the engine management light stayed lit while the engine was cranking. With the new sensor fitted the light extinguished the moment the starter engaged and started cranking the engine.
As already said the ECU doesn't run the fuel pump unless it can sense the engine is turning.