A business in Gidea Park is under investigation after allegedly selling alcohol to an underage customer.
Havering Council said the business will have its licence reviewed and its trading standards officers are working with it to create an action plan.
This includes providing education, support, and advice to prevent future underage sales.
The licence review may also result in additional conditions being imposed, a council spokesperson said.
The authority is not naming the business while its investigations are ongoing.
The action was taken after council officers made unannounced visits across the borough, checking that retailers were not selling age-restricted products such as fireworks, vapes, and alcohol to those under 18.
As part of the operation, 12 different premises in Upminster, Romford, Collier Row, Harold Hill, Gidea Park, and Hornchurch were visited by volunteers, all aged under 18.
The volunteers attempted to buy fireworks, alcohol, or vapes, all of which are illegal for purchase by those under 18.
Out of the 12 businesses visited, only one sold alcohol to the young volunteer.
Councillor Ray Morgon, leader of Havering Council, said: "Our teams are regularly making these visits, so we can make sure everyone is continuing to comply.
"We will always take the strongest possible action on those that don’t comply, which may include prosecution."
Any business found selling age-restricted products to those underage could face prosecution and the loss of their licence, the council said.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here