The move marks a tightening of the Met's already strict policy, which has seen applicants rejected for having the image of union flags and panthers on their arms.
Potential recruits previously had to supply photographs of any tattoos they have to see if they complied with the "dress code", with those deemed discriminatory or violent ruling them out.
But on Monday existing officers and civilian staff were sent a memo from the Commissioner making it clear that they must not get any more visible tattoos and must declare all those they currently have within a month - or face a disciplinary hearing.
The note said: "All visible tattoos damage the professional image of the Metropolitan Police Service. This corporate announcement discusses a specific requirement from the MPS Dress Code Policy in relation to the display of tattoos.
"With effect from the date of this announcement, tattoos on the face, or visible above a collar line, or on the hands are not permitted. All other tattoos must be covered.
"The MPS is aware that some officers and staff already have prohibited visible tattoos. These are defined as tattoos that can not be covered by everyday clothing (i.e. on the face, above a collar line and on the hands).
"It will be a requirement, by the Commissioner, that all officers and police staff with existing tattoos defined as 'visible' must register such tattoos as a formal written declaration to their line manager before 12 November 2012.
"Any officer or member of police staff who fails, without reasonable excuse, to declare and register an existing visible tattoo will be liable to disciplinary action. Such a failure is liable to be considered to be gross misconduct."
The new restrictions have been called into question by the chairman of the Police Federation of England and Wales, which represents rank and file officers.
Paul McKeever said: "I'm surprised to hear that the Met have made that statement without consulting officers."
He said there were "very few" officers who have tattoos on their faces or necks, but that the "diktat" could cause problems for former soldiers who have them on their hands.
"I wouldn't want to see any of them put in a position that causes difficulties as they're often some of the finest officers we've got."
Mr McKeever added: "I don't see how it could affect their ability to do their job."