All four are understood to be Asians living in London and are feared to have links both with Islamic extremists in Britain and worldwide terror groups - including Al Qaeda training camps in Pakistan and Afghanistan.
MI5 chiefs reportedly believe the suspected moles have been planted as sleepers - agents under deep cover - to keep Al Qaeda informed of anti-terror raids planned by London's Metropolitan Police (Met).
They are said to fear the four could have already accessed sensitive information about secret operations to root out terror cells planning further attacks in the UK.
The four officers are under 24-hour physical and electronic surveillance by MI5, including telephone wiretaps, and their financial activities are under investigation, the paper reports. Intelligence agents have created a family tree for each suspect with links back to their home countries, while agents are cross-referencing the suspects' names with lists of men that trained in terrorist camps in Afghanistan and Pakistan.
Scotland Yard refused to comment on the substance of the report. However, a source within Scotland Yard told the paper:
"We take matters of security very seriously and if any issues arise about individuals, they may be subject to further assessment.
"This could lead to restrictions being put in place relating to where an individual may work within the organisation or could lead to their dismissal."
"If there are people within the police force feeding information to terror groups this needs to be stopped.
"Since the names came to light there has been a non-stop effort to find out everything about their backgrounds."
Terrorist attempts to infiltrate Britain's police forces are nothing new, according to the article. The Irish Republican Army had some success placing agents into Northern Ireland's police force and army during the Troubles of the 1970s.
The Scotland Yard source admitted that sleeper agents are hard to root out because they have already been vetted and thus can fly under the radar.
InformationWeek's Security Weblog argued that if this story is true, it proves organizations have as much to fear from their own employees as they do from outsiders.
This goes to show that as much as governments, and even businesses, focus on outsiders, better precautions need to be put into place to ferret out insiders gone bad in the first place. Some of the worst examples of insiders inflicting enormous harm on the United States have been our own agents, such as Robert Philip Hanssen at the FBI and Aldrich Ames at the CIA.
But fear of infiltration by al Qaeda or like-minded organizations could harm the Met's ability to recruit a more diverse police force. Already, Member of Parliament Patrick Mercer, a terrorism adviser for the conservative Tory political party, told the paper that "Recruiting ethnic people into key public sector organisations - in place to protect us - is a risk."
As our January cover, "Fighting Terrorism in the U.K.," reported, the Met has stepped up efforts to recruit ethnically diverse Muslims into its ranks to earn the confidence and support of London's many Muslim communities.
As a source in the Metropolitan Police Authority, the Met's watchdog, told Security Management, police outreach "has a role to play in stopping bombs, just as detective work does."