Harrow, code 50U performing a prohibited turn - no U turn, High Road / Boxtree Road

Hi all, second PCN I'm looking at (last week was not good! And I'm getting married next week so can't really afford these fines!)

This one's from the London Borough of Harrow, a contravention of code 50U - performing a prohibited turn, no U turn - at the junction of High Road and Boxtree Road, recorded by a roadside camera.

Not going to sugarcoat this one, there were some roadworks up ahead so I changed my mind and turned around. I turned left from Boxtree Road into High Road, there is a no uturn sign but it's right at the junction as you turn on to High Road so missed this.

A few things I'd appreciate input on:
- What's the usual signage requirement for a no U-turn restriction to be enforceable - does it need to be at the point of the turn itself or is advance signage enough on its own?
- Is 50U one of the codes where Harrow has known compliance issues, I looked at the spreadsheet but didn't find anything.
- What's the best grounds to make a representation on?

Street View link:

PCN:



Video is hosted here:


Thanks again.