The legendary songwriter's music forms the basis of new stage show Close To You: Bacharach Reimagined, which launched at the Criterion Theatre in the British capital this week (beg12Oct15).

Burt attended the opening night show on Thursday, and later celebrated by setting up a stage in Piccadilly Circus, just yards from the front of the theatre, to perform a short set for hundreds of fans.

He was joined by members of the cast after they came off stage for a singalong with the crowd, and the street performance was documented in a series of pictures and videos posted on the show's account.

"Outside the @CriTheatre right now Mr Burt Bacharach & our cast with an extra special performance! #BacharachReimagined," one tweet read. Another message added, "Piccadilly Circus doesn't know what's hit it..."

"It's a great honour to have my music done like this and received like this," Burt says of the show. "Very emotional. It's a very good night for me."