London is currently clamping down on taxi touts - big time.
A tout doesn't stand outside the car shouting 'cheap ride home' to passers by. They know they are acting illegally and are discreet. The park up in busy areas, with their interior lights on, hoping to attract fares. Rather like you did.
Even if this man was somebody you know, it is still illegal to charge for the ride.
I would suggest you and your vehicle have been watched for some time - a bit of a coincidence you getting stopped the very first time you innocently give a stranger a lift. I also think this couple were undercover enforcement officers.
Frankly, your story is not convincing. If you were touting, plead guilty. If you weren't, hire a solicitor.