@SiSutts for a 2005 registration, we must be talking about an x244 model. (See VIN in registration V5C, on on VIN plate under bonnet over radiator.
Does the engine turn over with starter, but not fire? If yes then you could try the following, which worked for me.
I note that the code receiver and ECU have already been checked , but still worth a try?
Remove lower steering column cover. No.2 Pozidrive heads, easier to remove than replace because recesses are sloping. (I have a #2 Pozidrive driver with a piece of reinforced plastic fuel tubing on the shaft as a centering aid.) The upper and lower covers clip together, so some carful levering required.
With lower cover removed the code receiver is visible. Two connectors, the smaller one is 3 pole, with 2 ways used for aerial ring connection. Unplug apply electrical contact cleaner, then reconnect. For good measure treat the larger connector in the same way. Try starting before replacing covers. If still no ignition, then measure resistance of aerial via small connector. Should be about 30 Ohms. I suspect that many have been changed when only connector contacts needed cleaning, which the act of unplugging will partly do.
@RalphM has already suggested a possible ignition switch problem. I tried changing mine for a cheaper alternative from Ebay, and failed to get it to mechanically engage in the correct position. One of my few failures, as when one of the locating tabs broke, I gave up and purchased a more expensive unit which carried the original part number, and clicked into place without a problem. Attached is my own diagram, which includes part number, showing how it connects. On my diagram there is a connection across the switch where a black square or rectangle is shown.
Here is a link to a suitable part on Ebay.
