Beyoncé Knowles' security will reportedly be tightened at a London concert Saturday amid fears an alleged stalker will make an appearance.

The singer is currently in Europe performing her The Mrs. Carter Show World Tour.

According to UK newspaper The Mirror, there are mounting fears over an alleged stalker in Britain and her team is taking no chances.

The outlet reports more staff than usual will be looking out for Beyoncé when she headlines the Sound Of Change charity concert at Twickenham Stadium this weekend.

Staff have reportedly been told to keep an eye out for Bassey Essien, described as an 'obsessed fan'.

Beyoncé won an anti-harassment order against the man in 2011 after he allegedly sent her threatening letters claiming she murdered the real Beyoncé Knowles and was an imposter.

'Staff have been briefed on the situation and pictures of him have been passed around,' a source told The Mirror.

'They've been told to keep their eyes open and be extra vigilant.'

A spokesperson for Beyoncé has declined a request for comment.

On Monday night another fan got overzealous with the star.

Video footage at her concert in Copenhagen shows a male fan spanking her rear in the middle of the show.

She addressed the man directly before heading back to the main stage.

'I will have you escorted out right now, alright?' the singer said.

Other stars playing at the Sound Of Change event include Jennifer Lopez, Florence and the Machine, John Legend and Rita Ora.

Organisers aim to raise money to 'promote education, health and justice for girls and women everywhere', according to the Sound Of Change website.