Army tanker drivers are delivering supplies to petrol stations hit by the fuel crisis.
Around 200 military personnel are being deployed in Operation Escalin, with the troops to initially be concentrated in London and the South East, where the worst shortages remain.
Operation Escalin was originally drawn up in preparation for possible fuel shortages following Britain’s final withdrawal from the EU single market at the start of the year.
The drivers include members of 3rd Logistic Support Regiment who have been training with petroleum industry logistics company Hoyers in Thurrock, Essex.
Ministers have faced criticism for not sending the troops out earlier after a wave of panic-buying, but the Government has been deploying its reserve tanker fleet since last week in an effort to bolster supplies.
A government spokesman said: “We are working closely with industry to help increase fuel stocks and there are signs of improvement in average forecourt stocks across the UK with demand continuing to stabilise.
“Stocks in London and the South of England have been recovering at slightly slower rates than other parts of the UK, so we have begun deploying military personnel to boost supply in these areas.
“More than half of those who have completed training to make fuel deliveries are being deployed to terminals serving London and the South-East of England, demonstrating that the sector is allocating drivers to areas most affected in this first phase from Monday.”
The Prime Minister also said the crisis was “abating” and that the military were being deployed as a “precaution”.
The Petrol Retailers Association (PRA) has welcomed the deployment of the military, but has suggested it will only have limited impact.
PRA chairman Brian Madderson said although the crisis was “virtually over” in Scotland, the North and the Midlands, more than one-in-five filling stations in London and the South East were out of fuel.