It's true that the parts are easy to reach but you must be sure that they are to blame first. The 1.5 will not start easily from cold if the glowplug regulator is kaput, but it will when warm. If it is hard to start hot and cold, then the camshaft position sensor might be fouled.
Differentiating between these two issues is why (I believe) Tom asked his question. If the car is lacking power all the time and is hard to start whether hot or cold, the culprit is likely the camshaft sensor.
However, you might want to look at the manuals at the top of the problems forum. There are factory manuals and troubleshooting guides. Either or both codes could be indicative of something entirely different (or a common wiring issue).
Silver 08 plate 5dr 1.5dci Dynamique 106 Tech Run (re-mapped)
Red 03 plate 5dr 1.9 Dynamique dci120
Best advice for Megane owners: sell it before it bankrupts you!