Rover 75 1.8 - Engine turns but won't start

[EVS]

Hello everyone
Since I'm new here, first I'll give a bit of background on the car:

Back in January I was looking for a car to replace my old one, and I stumbled upon a 2004 Rover 75 Connoisseur midnight blue, 1.8 petrol. It had about 84.000 km, looked decent overall and the seller informed me the head gasket had been replaced already since the original ones were known to have issues. Sounded like a good deal to me, so I went for it.

First few months went by fine, I was happy as could be with my new car, until one day I'd stopped to refuel. After refueling, the engine wouldn't start right away. It started on the second try so I didn't think anything of it.
Later that day, I wanted to start my car again, nothing. The engine seemed to be turning, the starter's working away, but it did not fire up.

I took it to the mechanic's, who looked at the car for about 2 months but could not locate the issue. In order to avoid running up the costs even further, it's now sitting in my yard and even though it's a nice looking car, it'd be a shame to just have it sit there.

The mechanic only found one actual issue: the fuel pressure apparently isn't nearly what it should be. They did not find the source of this problem, however.
In my own search for a possible cause, I came across this forum and consequently looked at the fuel filter. It does not have the orange clip, but both parts still seem to be together pretty well.

Do any of you maybe have an idea of any possible causes for this problem? When turning the ignition, the rev-counter does move, but the engine won't fire up. Sometimes it sounds as if it's starting for just a second, but it never actually runs.