TD5 won't go over 50 suddenly

Weeks ago I drove a good 90 mile trip, got there fine. Turned the car on to come home and the engine was sluggish and stuttered at high revs in each gear and topped out at 50 then started loosing power. 45mph all the way home. Turned off and on.. struggled to start. Sat stationary for a week. Drove 3 hrs on the motorway yesterday and it was perfect, no problems. Today.. Problem eturned! It's an 06 TD5 defender. And ideas?

Turbo wastegate seized?

Fuel cap vent blocked?

Sediment in fuel filter? Unlikely but worth a check

Air Flow Sensor ?? Try unplugging it and see if power returns - I had that happen on mine and the sensor was faulting

any warning lights on ?