Corsa no power, emissions light, judders and stalls

Help!
I've been to 3 garages now, a friends dad, and 2 AA men look at my car. Ive just picked it up from my local garage at a cost of nearly £300 and they couldn't find a fault.
The car is a vauxhall Corsa. The emissions light was coming on, flashing and then I'd get no power. Didnt matter if I had my foot on the floor, I could only reach 60mph max, and then if I slowed down, it would stall and sometimes not start again. Seems to only do this when it gets hot (motorway driving)
The mechanics have done a diagnostic check, changed the fuel filter, the coil and the 02 filter (?) and they say its still not solved the problem so they've said they cant do any more! Help me please! Tempted to get rid, but its only an 05 plate.

Change the crankshaft sensor (they're about £30).

Air flow sensor / MAP sensor would spring to mind.

Not always picked up on the fault codes as it may still be within tolerance
when the ECU does its check.

But you would have thought your friends dad would have known that?

Crank and cam sensors out of phase maybe?
Seem to be getting a few of these just now - Nissans particularly
John

I had similar symptoms on my mothers old Astra. It turned out to the catalytic converter was blocked and it couldn't breathe properly but I would suspect that if its 05 then you should not have those sort of problems! unless perhaps it had covered some miles?