Ahhhh, Big Mel, such fond memories. I had the same Rover 3 ltr as Gently drives, and then had the 3.5. V.8. P5. Coupe with the Rostyle wheels. It was like driving around in your favourite armchair, I also remember watching the petrol gauge going down, but in 1967 when I had the 3ltr I didn't mind too much as petrol at the local Jet garage was 4s. 1d a gallon. (20.5p) NOT a litre, a gallon.......
I was working at Vauxhalls Luton when the Viscount was being made... Swore I would 'NEVER have a Vauxhall'... 
I had a friend who had a 3.3? litre Viscount auto. Frightening fuel consumption. He used to drag race it from lights holding it on the footbrake while he wound the throttle up.
I have fond memories of a lot of the other cars on the TV series. As young teenagers we seemed to have access to an inexhaustible supply of "wrecks" to go tracking in off public roads, maybe the MOT had just come in and condemned a lot of cars. Our parents would have had heart attacks at some of the escapades. I remember a mate getting six of us into a big engined Westminster (Rolls Royce I think?) and hurtling around a field of stubble. We came to the end and he threw it into the corner (like you might with a well sorted rally car. It responded, predicatably looking back, by rolling a lot into a hedge. We all thought it was a great laugh - no injuries apart from bruises. The car was a right off.
Had a Sunbeam Talbot 90 for a while. Great car - would be worth a bit now.