Theresa May has said she hopes that a way can be found for all England football fans to be able to show their support for the team by flying flags during the World Cup.
Her comment came after it emerged that postal workers have been told not to fly the Cross of St George on their vans during the tournament, which begins in Russia on Thursday.
The Royal Mail said a policy in place for a number of years allowed workers to display flags in offices, but not on vehicles.
Mrs May's official spokesman told reporters: "The Royal Mail's policies are a matter for them.
"But the Prime Minister believes everybody should be able to show their support for the England football team and hopes a way can be found for people to do that.
"The Prime Minister wishes the England football team the very best and hopes the country enjoys cheering them on."
A Royal Mail spokesman said: "Flags should not be flown on vehicles as Royal Mail has a duty of care both to all employees and to members of the public.
"This is a company-wide policy across the business, which covers flags and stickers across trollies, bikes, vans and lorries. No other flag or insignia should be carried next to the Royal Mail brand and insignias.
"Flags placed on vehicles can obscure the driver's view. They can also pose a potential hazard to other road users if they are lost when the vehicle is moving.
"We do want our colleagues to have every opportunity to follow the World Cup but we need to continue to provide services to customers.
"There will be flags on display in Royal Mail offices and live radio commentary playing on PA systems during matches."