Two in three parking tickets are illegal

Give someone a uniform and a modicum of power and there's a good chance things are going to go pear-shaped. Anyone who has ever remonstrated with a traffic warden hovering over their car as the last seconds tick down on their parking meter, or come back to their car parked less than an inch onto double yellow lines to find themselves a hundred pounds or more poorer will testify that a little bit of power can easily go to some people's heads.

But it's worse than that, one group of campaigners is claiming that the power is so intoxicating that traffic wardens are giving out up to two thirds of their tickets illegally. So what's going on?