What do Those Signs Mean?

Entering Westbourne Gardens with a motor vehicle for any purpose other than to visit properties between the 619/620 signs at both ends of the street is a moving traffic offence under Road Traffic Act 1988 Section 36  - "failure to comply with a traffic sign" - in essence the same as jumping a red traffic light.  The sign must convey a statutory prohibition and be established by relevant legislation (Which they do). There is a statutory presumption that a sign is sufficiently authorised unless proved to the contrary. Westbourne Gardens has been"Access Only" for over 40 years - in fact 42 years since a Traffic Regulation Order in 1971.

Contravention of the signs would normally attract a fine and an obligatory 3 penalty points if tried summarily at a Magistrate's Court and and optionally a disqualification - one has to assume in worst cases. The Police apparently have the discretion to issue Fixed Penalty Notices to avoid judicial process..

The CPS guidance is here , specialist traffic solicitors advice here  

Contraventions under Section 36 of the Road Traffic Act 1988 can be proved by the evidence of only one witness as the need for corroboration does not apply.

As a public service we can recommend www.keepmedriving.com if you are caught.