Beyonce Knowles has beefed up security for her concert in London this Saturday after threats from a stalker and the infamous booty slapping incident that occurred in Denmark earlier this week.

Bey will perform at Twickenham stadium as part of the "Sound Of Change" concert, and staffers will be on the lookout Bassey Essien, who has reportedly sent the singer nasty letters. A source told The Sun, "Staff have been briefed on the situation and pictures of him have been passed [around]. 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."

Essien tracked down Beyonce at an event in London in 2009 and tried to give her a collection of notes on religion, and he was later charged with an anti-harassment order by the High Court in 2011.

However, Essien isn't the only reason Bey is looking for more muscle .. apparently the 31-year-old singer was furious after a male fan reached up and slapped her on the derriere at her Mrs. Carter Show world tour in Copenhagen, Denmark, on Monday night. I guess he didn't realize that was a Jay-Z only privilege! In case you missed it, check out the video below: