//If the vehicle isn't moving than as far as I define driving, it's not being driven.//
Alas your definition differs from the established legal one, OG. That said, there is no statutory legal definition. Instead, each case will turn on the facts and those adjudicating will be guided by precedents. Here's a couple on which prosecutors may rely:
In Pinner v Everett (1977) 64 Cr App R 160 Lord Upjohn said (in respect of whether P was a “person driving or attempting to drive” at the time he was required to provide a roadside breath test) “It is not necessary that the vehicle should be in motion. A person is obviously driving although he may be in an almost interminable traffic block or waiting at a level crossing or at traffic lights, or if he merely fills up with petrol; nor can it make any difference if in a traffic block he switches the engine off to prevent it overheating or to save petrol.”
In Edkins v Knowles (1973) 57 Cr App R 751 The Divisional Court summarised the case-law on the subject of when “driving” ceased:
The vehicle need not be moving. Once it has come to rest the operations of applying the handbrake, switching off the ignition etc. should be considered as part of the driving; Has the motorist reached the end of their journey? Subject to the brief interval needed to carry out the operations referred to above then on reaching the end of the journey they should no longer be regarded as driving;
When the motorist stops during the journey the following questions will be relevant in deciding whether they are still driving or not:
Is the purpose of the stop connected with the driving?
How long was the stop? The longer it was the less likely it is that they can still be considered to be driving;
Did they get out? If not, that is an indication (although not conclusive) that they are still driving. When a motorist has been effectively prevented or dissuaded from driving then they are no longer to be considered as driving.
All this means that an individual stopped at a traffic light or held up in traffic could be prosecuted for a mobile phone offence.
Finally, some guidance to CPS prosecutors:
"However, prosecutors should bear in mind that the intention of the legislation is to promote road safety. They should ask whether the use of the phone or other device is in circumstances which might prejudice the driver’s ability to drive safely."
"A person who uses their phone while stationary at traffic lights will be distracted and less able to move off safely when the light change. Similar considerations would apply to a driver stationary in a traffic jam."
"However, although the House of Lords in Pinner v Everett held that a person might still be driving even when they turned off the engine and got out of the car it is unlikely, other than in exceptional circumstances, to be appropriate to use section 41D to prosecute any person who in these circumstances made a phone call or accessed the internet."