As for Lane Markings these help:
https://www.gov.uk/guidance/the-high.../road-markings
Picking up on "Information" (and this applies at all roads) you'll mostly see "Lane Dividers" the short line followed by a large gap.
If this changes then that's Information to used. There are, of course, technical standards about the width of the line, its length, the distance between them etc.
So, if the lane divider becomes a "Hazard Warning Line" (the opposite of a lane divider, long line, short gap) then there's a hazard of some sort up ahead. That hazard, in this case, is the slip road.
I'd want to be in the correct Lane as soon as possible after the hazard line starts and earlier if there's other Information to help out with Position.
I use a different plan of action to Number 6. ".....You use the markers to adjust your speed
and position (my highlighting) on the approach to the "Slip Road....."
I'd rather have about a minute to get into
position (From the information - the Road Sign) than using the 3, 2, 1, exit markers which at 70mph gives just 9 seconds to get into
position.
Obviously you make your own choices and create your own plan. Think of all those Police Camera Action shows where we see someone in Lane 3 diving across to try and make an exit.
If I've misinterpreted then apologies in advance.
For fun, have a look at the lines on some roads you know and see what changes and when it changes, particularly where there are bends, dips, crests etc.
And one tip.....
Generally the more markings on the approach to a hazard, the greater the danger.