Britney Spears has admitted that the drug fumes were so strong in one of her recent shows that she ended up “contact high”.

The Oops!…I Did It Again singer has a residency, Britney: Piece Of Me at Planet Hollywood in Las Vegas, which began in December 2013 and is set to run until May 2017, but said that spending so much time in Sin City could sometimes affect her own more virtuous lifestyle.

Speaking on The Jonathan Ross Show, she revealed: “I am aware of the partying that’s going on. A lot of the people are very intoxicated during the shows.

Britney has a Vegas residency (John Salangsang/AP)

“I actually got contact high. I haven’t smoked weed since I was like 17 years old and all of a sudden, towards the end of the show, it was so strong I couldn’t function because I just got the contact of it.

“I was like, ‘Oh my goodness!’ I had to leave, I had to go. I kinda just said, ‘I can’t do it anymore’.”

Britney, 34, added of Las Vegas: “There’s parties all around. I just don’t go in there, they’re private parties. There’s a lot of drugs involved.”

Britney is known for her stage shows (Chris Pizzello/AP)

Despite her hectic performing schedule, Britney said she was able to get on with normal life by drawing a line between her stardom and everyday tasks.

She explained: “I have this thing where I’ll go into denial a little bit and I’ll put this hat on and I’m like everybody else.

“It really usually works because no one pays you any attention. It’s like a disguise. I’ll just take my dog for a walk or I’ll go shopping or I’ll do normal stuff.

Britney is on The Jonathan Ross Show on Saturday (Jordan Strauss/AP)

“I’m used to my show, it’s like a character change. I’m a performer so I know how to mentally adjust my head to go there in character. It’s not me, it’s not who I am at all but it’s part of what I do.”

Britney appears alongside Emily Blunt, Luke Evans and Alexander Skarsgard on The Jonathan Ross Show on ITV, Saturday at 10.20pm.