If due to an accident, breakdown or physical malaise we had to immobilise the vehicle on a motorway or dual carriageway, may the occupants of the vehicle walk along the carriageway to ask for help at the nearest emergency post?

The occupants of the vehicle may under no circumstances walk along the carriageway of a motorway or dual carriageway, not even wearing the approved vest.
The carriageway is the part intended for the circulation of vehicles, so it would be a huge risk to walk there, especially considering that on motorways and dual carriageways one drives at high speeds.