I also know of someone who parked on Tongdean lane whose car was towed away during a game after a steward had asked him not to park there, so they may have a little more power than you give them credit for.
Just to make clear, stewards do not have the power to get people towed. They might have informed the police of someone obstructing but it was the police who had the power to tow. And to be frank it's deserved if it is obstruction.