Yes it is an offence to obstruct a driveway. Highway Code Rule 242, page 82. Road Traffic Act 1988, sects 22 and CURb reg 103. Section 86 of The Traffic Management Act 2004 states "The second exception is where the vehicle is parked outside residential premises by or with the consent (but not consent given for reward) of the occupier of the premises. This exception does not apply in the case of a shared driveway." But how does a passing traffic warden know the car is registered to the address without accessing the Police national Computer?