tempted towards direct action...

[Vorpal]

When it comes to taxis, I tip taxi drivers who drive according to the law, and don't tip those who don't. And I am clear, when I pay them why they are receiving or not receiving a tip.

If it's a company that I use more than once, I find that after I've done this a couple of times, all of the drivers from that company know that I will tip them if they obey the law. I don't have much occasion to use London taxis, but I had just flagged one down, I might explain my system in advance to give the driver a chance of earning a tip.

I have also refused to use taxis according to queuing custom at the station a couple of times, and waited for the front of the queue to clear of taxis from a company I didn't want to use. And I told them that I would not use them because a driver from their company had nearly run me over on my bicycle, and I wanted to make certain that that person never had any of my money.

As far as standing watch on bike boxes, traffic lights, or speed zones, I suggest that you talk to your parish council or local policing unit.

I seriously doubt that if you don't speak to the police in advance, and work with them, that you will get their co-operation afterwards.

The police in some areas already have some programs that allow volunteers to do various things (such as use speed radar guns). These programmes usually result in people receiving nice little letters from the police that warn them about their behaviour. I don't believe that it will normally result in prosecution.

[thirdcrank]

... As far as standing watch on bike boxes, traffic lights, or speed zones, I suggest that you talk to your parish council or local policing unit. ...

And before you do so, rehearse the line you intend to take on non-observance of traffic lights more generally.

[Big T]

I've often thought that it would be good to have some statistical evidence of traffic violations. This could be done by standing at various junctions and merely recording the number of drivers that commit offences during an hour. You could also do this for cyclists, so when the argument is raised that cyclists all RLJ you can say "Well actually....only X% do this, whilst Y% of drivers infringe the ASL, Z% speed (there's plenty of indicative speed signs about now) W% use a mobile phone whilst driving, etc.

If anyone queries what you are doing, you can then say that you are just gathering statistics.

[reohn2]

Slightly off-topic anecdote:

I was in Cambridge shooting some video of bollards going up and down. The camera was on a tripod with a telephoto lens focused on the bollard. The bollard on the other side was broken in the down position, so any motorists could get into the city centre.

While I was still setting up and the camera wasn't on, a car approached the bollard I would be filming, trying to get out of the city. The bollard stayed up, blocking him. It wasn't a taxi and I supposed he didn't have a permit to be there. The car went back and forth a few times but the bollard stayed up.

Then the driver figured out that the bollard on the other side was permanently down so he reversed and moved over to the other side. Just before he went over the bollard, a taxi driver pulled up and shouted, "I wouldn't do that, there's a bloke over there filming you."

The errant driver looked sheepish, turned his car around and drove back towards the city centre. Perhaps he's still there, searching for a way out.

Nail,head,on.
If people who break the law thought they'd get caught and it cost enough to hurt,they wouldn't do it.
As it is they know there's every chance they won't and so do.
If anyone thinks such people's conscience will be pricked by pointing out the error of their ways,think again it won't,you're more likely to receive a stream of abuse and in some cases worse.