TD4 - very regular missing/hesitation

Strange problem started last summer, ceased abruptly in Oct last year and has now started doing it again.

Symptoms occur with clockwork regularity - after sitting overnight, about 6 miles into a journey, the car will hesitate whilst cruising and each hesitation will be accompanied by the engine management light flicking on. It does this for about 3 miles, then it completely clears up. On the return journey, after sitting for best part of the day, it will do exactly the same, always without fail about 6 miles or so into the journey. You can almost predict at what bit of the A1 it is going to happen! The light never stays on, only during the hesitation.

I guess I need to get a diagnostic test, will a fault code be stored, even if it is an intermittent sympton? It is very strange that it is so regular, and seasonal, it seems! It also seems to co-incide with the engine reaching proper temperature, just after warm-up.

Can anyone offer any clues?

My engine management light came on last year,it went off when I removed the air filter.I found there was a leak in the flexi joint in the exhaust,the fumes had clogged the air filter.
This of course might have nothing to do with your problem.