Breakdowns – highway code rule 274

If your vehicle breaks down, think first of all other road users and

get your vehicle off the road if possible
warn other traffic by using your hazard warning lights if your vehicle is causing an obstruction
help other road users see you by wearing light-coloured or fluorescent clothing in daylight and reflective clothing at night or in poor visibility
put a warning triangle on the road at least 45 metres (147 feet) behind your broken-down vehicle on the same side of the road, or use other permitted warning devices if you have them. Always take great care when placing or retrieving them, but never use them on motorways
if possible, keep your sidelights on if it is dark or visibility is poor
do not stand (or let anybody else stand) between your vehicle and oncoming traffic
at night or in poor visibility do not stand where you will prevent other road users seeing your lights.