Robbie Williams blames his forgetfulness on his past drug use.

The 'Let Me Entertainment You' hitmaker uses autocues to remind him of his lyrics as he ''suffers with anxiety'' through a ''high-pressure scenario''.

Speaking to The Sun on Sunday newspaper, he said: ''Now if you were in a stadium full of people and you had done drugs in your life, your brain is not going to be working properly. And the last thing you want to do when you are staring at 80,000 people is go, 'Yep I do not remember these words.' That's why I got an autocue because I suffer with anxiety and it is a high-pressure scenario.''

Meanwhile, Robbie previously confessed he was ''unable to leave the sofa'' for three years as he battled agoraphobia.

The 45-year-old pop star has admitted the anxiety disorder - which causes people to avoid places or situations that may trigger panic - left him housebound for years.

He shared: ''My career had gone stratospheric and taken me to Mars, and I needed some time to get my equilibrium back and get myself back together. It was my body and mind telling me I shouldn't go anywhere, that I couldn't do anything. It was telling me to just wait - so I literally just sat and waited.

''I was agoraphobic from around 2006 to 2009. Those years were just spent wearing a cashmere kaftan, eating Kettle Chips, growing a beard and staying in. I remember they offered me £15 million to take over from Simon Cowell on 'American Idol', plus a big gig in the States, but I turned it down because I wasn't leaving the sofa at the time. I just couldn't.''