I was under the impression that all time spent at the wheel of your vehicle with the engine running counted towards driving time on your tacho but according to an agency driver at our place if you are sitting stationary in a traffic jam say for 5-10 minutes this counts as other work. He says that because you are not steering the vehicle you are not driving. Surely you are still in control of the vehicle so this must count as driving time. We use analogue tachos at the moment…I don’t know if the way driving time is recorded on a digital tacho is different. If he is correct then my colleages and I are mistakenly pulling over on the A1M for a 45 minute break on our way to our Yorkshire depot from Bristol because we will be over our hours by 10-15 minutes after being stuck stationary in traffic. Please let me know who is correct.
My take on this is that technically you are in control of the vehicle, therefore driving if it is on the public highway. However, the tacho only records movement of the wheels, so would record other work (or whatever your analogue tacho is set to) when stationary. I don’t know what the VOSA take on this is - it is quite a grey area I would imagine, as sitting in a queue for a few minutes is not really the same as being on stop for say 20 minutes. I suppose it’s “how long is a piece of string?”.
On a normal drive I use a timer and assume that driving starts when I leave and ends when I stop. That way I’m always under on the tacho. If I am stopped for more than about 5 minutes with no sign of moving I may stop the timer.
But I’m sure someone with expert knowledge will be along shortly with a difinitive answer.
COFFEE!!
Court ruling from the 1990’s is that if you are sitting behind the wheel in order to control the movement of the vehicle then you are taken to be ‘driving.’ The definition given in the new Drivers Hours rules is that if the tacho says’ you are driving, then you are driving. But as Gardun said; tachos record vehicle movement, they cannot work out if you are sitting behind the wheel of a stationary vehicle.Strictly speaking driving would include you being startionary for 20 minutes in the traffic jam. However, a digital tacho will record ‘work’ after a period of driving, unless the driver uses the mode switch to select another activity. Analogue tachos will record whatever the mode switch is set at when the vehicle isn’t moving (unless you have a very old tacho with a 4 position mode switch). I think it would be fair to say that most officers would regard you being stationary in traffic for any time as work, won’t necessarily be POA as you don’t know how long you are going to be there.
You could sneak the mode switch onto ‘break,’ afterall, who really knows where you are and what your doing, but I couldn’t possibly tell you to do that 
Personally, right or wrong, I count any time spent stationary that’s under 15 minutes as driving time EXCEPT when I’m doing a quick drop and have paperwork to prove that it was a delivery.
All the time you are sitting behind the wheel with the engine running counts as driving, I know this because in my job I frequently have to wait in queue of vehicles moving maybe only a few yards at a time and there ain’t no way you could take a break from controlling the vehicle… 
Unless you are on digi and after 2 minutes of non movement , those 2 minutes of non movement and any time after that will be automatically recorded as other work .