D2td5 lacking power when cold. help!!!

Hi all
Im having problems with my td5 disco. In a morning or when the engine is cold ig is will only rev to 2500 3000 rpm untill the yellow light for the rear fuel filter that tells yiu there is water in the filter flashes and instantly its fine and drives like notmal.
To date ive changes the aire flow meter and the rear fuel filter.

Why is this happening? ?...

Not sure what's happening there. Check stuff called protech line cleaner. Have a look at this. My friend is a mechanic and he says that this stuff is the dogs tool. I put it into my td5 and its going like a train.
Look here.

Gas or Diesel Fuel Cleaner | PRO-TEC Autocare | Best Fuel Cleaner of 2013 - YouTube

Might be worth a go.

Problems solved it ended up being a nackerd fuel pump relay. The contact was all warn