Vauxhall Astra cutting out at speed

when I take the car over 50mph accelerating reasonably hard, ill put the car in any gear depending on the speed I’m going and just tickle the revs the car begins to jerk and shudder once this happens I could be driving at any speed and pull the clutch in and the revs will drop below 1000 and cut out, bringing on all the dashboard lights as if iv just turned on the ignition. If I come to a stop and try starting the car it won’t do until I apply the accelerator and the problem will still persist. Sometimes after this problem occurs I can pull the clutch in n the revs will bounce from 1000 to 4000. But it tends to stop doing all this when I come to a complete stop and I put it in first and set off quite vigorously. Mechanics haven’t got a clue n no fault codes appear on the laptop any ideas?