rj2dj - Member
The DVLA will already know it's not taxed and be sending an automated letter to them to fine the registered owners for not SORNing it.
Reporting it to the DVLA won't get it moved. If it's actually obstructing the road (eg: Fire appliance couldn't make it past) then report it to your local police.
EDIT: To say, if it is already SORNed and on the road (you have no way of knowing this) then the police might be interested.. but I feel it's unlikely.
The police won't be interested unless the car has been reported stolen, is known to have been used in a crime or otherwise has a tag against it.
You should report it to your local (borough) council. They will fix a removal notice to the windscreen which gives the owner seven days to move it. If it hasn't been moved by then, then the council become responsible for it and will/should impound it.