Maq, do you have any update on how the car is doing now that it has been 2 months or so?
I have a 2.2 dCi Laguna Dynamique.
I have the same issue and it is getting annoying. When I get to 70mph or so when joining a motorway after the slip road I will get the light. The power then seems non existant. If I come to an incline its a real pain, on flats it is bearable but still nothing like it should be! It then stays on till I can stop and turn the ignition off. However, get to 70 again and it will return.
Had my local mechanic check it out and the computer he connected was saying some issues with the Air Flow sensor. He said he found some sort of air leak and replaced the upper engine gaskets. 2 day job and he charged £160 for parts and labour.
However, the problem is still there! Also the car now consumes more fuel, it has gone from 43mpg to 32mpg for motorway driving! At one point for town driving it was showing 10mpg.
I have the car booked in with him for the timing belt in a few days. If your solution has worked I can print the information off and show it to him.
Any advice would be much appreciated.