White van men

There's often been scepticism that the BBC "detector vans" actually do the job - a suspicion that the equipment inside and on top of the old vehicles were props borrowed from early episodes of Dr Who. Now an FoI response confirms that the BBC has invented and manufactured gizmos that can find televisions in use - but can't exploit them commercially. That would require a patent - which would make public how they work - and allow licence-fee evaders a chance to work out how to block them.