Agila 1.2 16v (2003) - no compression in cylinder 2, and very low in cylinder 3 and 4

Hi there. First post here. I hope someone can shed some light. I've got a 2003 Agila 16v.

It was running well until a few weeks ago. Then suddenly no power. Starts, but only just, Doesn't keep running.

A mobile mechanic ran a diagnostic and the only fault codes were cylinder misfires. We changed the coil pack and spark plugs but that made no difference. .

I have since taken spark-plugs out and checked for spark. All four plugs have a spark.

I've taken fuel line off and checked for fuel at the engine end. There is fuel coming into the injector. I've also checked the pressure relief value on the end of the injector and it releases fuel.

I then did a compression test on all four cylinders. Cylinder 1 was 150PSI, cylinder 2 was 0, cylinder 3 was 25, cylinder 4 was 25.

I then did a wet compression test and the pressure readings are the same. Apparently this points to valves? Or associated components?

Obviously lack of compression is the problem - but I'm not sure what is causing it - slipped timing chain? Broken valve? There were no other issues or warnings or noises (except lambda sensor flashing the week before - which went out after I changed a flat battery).

Any experience or help would be appreciated.

Thanks
John.