Of all the vagaries of UK traffic law, the one I’ve heard most interpretations of has to be the “White Line” rule. That’s the one referring to white lines painted on the roads, just in case anyone’s getting ideas. Having read the Highway Cod very recently, I’d gotten it into my brain cell that you were allowed to pass agricultural vehicles at less than 20mph when there’s an “R” in the month, or something like that. I was tested and almost found wanting last week, when Captain Cardigan and I were hopping along a long queue of traffic that had built up behind a very slow-moving tractor/trailer. Normally, on my blithe ‘understanding’ of the Highway Code, I’d simply have popped past it without a second thought, if safe to do so, white lines or no. Our minds were however concentrated by the fact of the vehicle behind the tractor being a Police car. At which point, doubts they do surface. So we didn’t, and played good little bored road users until the road cleared.
When I got home, I did in fact get out my Highway Codes, all three of ’em, from 1987, 1993 and 1999. And yes, the wording has changed in the period. The trouble is, the wording I was remembering turned out to be entirely fictional. So I now stand sheepishly corrected. But at least not ticketed. So read the rest for the sordid details…

And this is what my three versions of the Highway Code have to say on the subject:
1987: Where there are double white lines along the road and the line nearer you is solid, you must not cross or straddle it except when you need to get in or out of premises or a side road, or when you are ordered to cross the lines by a policeman or traffic warden, or when you have to avoid a stationary obstruction.
1993: Where there are double white lines along the road and the line nearer you is unbroken, you MUST NOT cross or straddle it unless you need to get in or out of property or a side road, or avoid something stationary blocking your lane.

I guess they’d given up by then on expecting the police to be around when you needed them.
1999 on: Double white lines where the line nearest you is solid. This means you MUST NOT cross or straddle it unless it is safe and you need to enter adjoining premises or a side road. You may cross the line if necessary to pass a stationary vehicle, or overtake a pedal cycle, horse or road maintenance vehicle, if they are travelling at 10mph or less.
So, apart from the “D’uh” clause (“unless it is safe to do so”), the main change is in allowing you to cross to overtake particular classes of vehicle if they be moving at less than 10mph. Please note that this doesn’t include tractors, something I occasionally need to remind myself of.
And I am informed that a queue of cars waiting at a junction does not constitute ‘stationary’. I’m less sure about a static traffic jam and tend to make executive decisions at such times.
It also appears that, from 1999, you may enter premises or a side road, but you MAY NEVER LEAVE. Hotel California, anyone?
for the latest wordings from the (slow) horse’s mouth, check out the UK government’s Highway Code site.