if the driver has stopped for the purpose of complying with regulation 16, 17 or 19(b);

if the driver is prevented from proceeding by circumstances beyond his control or it is necessary for him to stop in order to avoid an accident; or

for so long as may be necessary to enable the vehicle, if it cannot be used for such purpose without stopping in that length of road, to be used for fire brigade, ambulance or police purposes or in connection with any building operation, demolition or excavation, the removal of any obstruction to traffic, the maintenance, improvement or reconstruction of that length of road, or the laying, erection, alteration, repair or cleaning in or near to that length of road of any sewer or of any main, pipe or apparatus for the supply of gas, water or electricity, or of any telecommunication apparatus kept installed for the purposes of a telecommunications code system or of any other telecommunica&£255;&£169;tion apparatus lawfully kept installed in any position.