The smoothie performer, once hailed by Frank Sinatra as “one of the major singers of our time”, proved less than impressive when he played at The Sage Gateshead on Tyneside on Tuesday evening.

As he sang in a packed venue as part of his big band 50th anniversary tour, some felt that Jack – one of the biggest stars of the Sixties and Seventies – was “a shadow of his former self”.

“He wasn’t polished or slick at all,” said one disappointed audience member. “He forgot the members of the band’s names and didn’t know the order the songs were coming in. He was all over the place. His voice was still good but he definitely wasn’t as impressive as he used to be.”

And it seems that even Jack – who was romantically linked with British actress Susan George during the Seventies – knew his performance was going downhill.

“When he did forget the words during some of the songs, he would just giggle. At one point he even excused himself by saying it was a new routine.”