Beyoncé steps up security for London show amid British stalker fears Security surrounding American singer Beyoncé has been stepped up amid fears of a British stalker as she prepares to make another appearance in London. The "Single Ladies" singer is due to perform at Twickenham stadium this weekend as part of the Sound of Change concert. Staff have reportedly been told to look out for a British fan called Bassey Essien who has been sending the former Destiny's Child star threatening letters labelling her an imposter. A source told The Sun: "Staff have been briefed on the situation and pictures of him have been passed round. They've been told to keep their eyes open and be extra vigilant. Security has been increased on a few engagements now, especially for her UK promo. It is believed similar letters to the ones that Essien sent have been received. Beyoncé, 31, was previously accosted by Essien at a function in London in 2009. He is alleged to have been trying to give her a book of notes he had made of his religious findings and claimed to have been "attempting to help the singer." Bassey was given an anti-harassment order by the High Court in 2011 following a number of other failed attempts to impose such a restriction on him. Essien suggested in his letters that the "Crazy In Love singer" was a fraud who had killed the real star, according to court papers filed at the time. Beyoncé had her bottom slapped by a male fan during a performance earlier this week in Denmark. She is reported to have told him:"I will have you escorted out right now, alright?" Beyoncé, mother to 16-month-old daughter Blue Ivy, whom she had with her rapper husband Jay-Z, is on tour with her family and large entourage. The performer recently made appearances in Birmingham and at London's 02 Arena as part of a worldwide tour. She is lined up to headline V Festival in August.