Ah OK - cheers for that Lamble
I make you right and as Geoff points out, it's pretty much impossible for a streetside policeman to know every nuance of the law, so why push it? If it's something that could be a grey area, it's not worth the hassle.
Putting my brain in gear, I guess I should've known that anyway... I've seen some pretty impressive stopping by police cars in high speed pursuits, alongside a car stopped at a zebra... i.e. they'll go past everything else in the queue, but they'll do whatever they can to stop at the front... then the poor old pedestrian gets all confused and doesn't know whether to carry on crossing or return to the comparative safety of the pavement!