Home Secretary Priti Patel is reported to be taking over the security minister’s brief only hours after the opposition Labour Party criticised the government for failing to fill the gap.
National newspaper The Times says she has been covering the portfolio since James Brokenshire stepped down to focus on his treatment for cancer.
Boris Johnson was expected to name a replacement later this year but earlier this week shadow security minister Conor McGinn said it “beggared belief” that the role had not been filled.
Labour said that the arrest in Berlin of a British embassy employee suspected of spying for Russia raised “questions” about the failure to appoint a new ministry to oversee the security services.
The security minister's responsibilities include counter-terrorism, serious and organised crime, cybercrime, economic crime, hostile state activity, extradition, and royal and VIP protection.
Mr McGinn said: "This is a clear sign that the Conservatives don’t take the safety of our citizens seriously enough. Rather than No 10 and the Home Secretary briefing against each other, Britain’s security should be the government’s number one concern."
"Getting rid of a specific, day-to-day, senior government minister responsible for security and counter-terrorism when Britain’s national security is under threat 24 hours a day, seven days a week is an abdication of responsibility," he added.