If johnny37 was right, there would be no speed cameras. Committees, which usually have a nominal police involvement, now operate mobile and static speed cameras. It is unlikely that the vigilantes would acquire evidence of the quality required in court, but in theory it could be used, although they would probably require police assistance with such matters as the calibration of the cameras. I can't see the police being enthusiastic about receiving a heap of information from the vigilantes that they were then expected to sort out and use for a prosecution. Thankfully, I have not seen these vigilantes for some time. In trying to make their point, which is sometimes invalid, some cause more danger to themselves and road users than the speeding does.