The furry-hatted and red-uniformed sentries that visitors to London like to be photographed with have been withdrawn from their sentry posts outside royal palaces for fear of falling prey to lone-wolf terror attacks, British media reports say.

The elite soldiers who make up the Queen's Guard in the British capital no longer stand alone outside Clarence House, St James' Palace, Windsor Castle and Horse Guards Parade.

They have moved to positions inside closed gates or when present are closely guarded by armed police, the Daily Mail reported.

At Clarence House, the official residence of heir-to-the-throne Prince Charles, guardsmen and their sentry boxes are now behind the railings rather than in the street in front of them.

It is now unlikely that tourists will be able to get close enough to pose for photographs with the Queen's Guard.

The first to report the change was Royal Central, an independent website that covers royal family matters.

Last month police chiefs in the central England city of Birmingham warned officers not to wear their uniforms to and from work as they said terrorists were looking to target officers who were alone.