Am I allowed to use a hand–held mobile phone if I am stationary in a traffic jam?

The simple answer to this is that no you are not. The definition of driving includes those occasions when the vehicle is temporarily not moving – for example in a traffic jam or at traffic lights. However, if the stoppage is a lengthy one – for example because the road is temporarily closed or there is no chance of traffic moving imminently and you have switched off your engine, then you may be able to use a hand-held device safely.