Stage impresario Sir Cameron Mackintosh has bought two West End theatres and announced ambitious plans to renovate one and rename the other.

Sir Cameron, whose successes include Les Misérables, The Phantom of the Opera and Mary Poppins, is taking over The Victoria Palace Theatre in central London next month and the Ambassadors Theatre by next year.

The latter will be renamed The Sondheim Theatre, in honour of the American composer and lyricist Stephen Sondheim, and The Victoria Palace will be closed for around a year for redevelopment including extending the stage and overhauling the auditorium and exterior.

Buying the two venues from Sir Stephen Waley-Cohen takes the number of theatres Sir Cameron owns to nine.

He said: “What really made the Victoria Palace irresistible to me is that Stephen has imaginatively seized the opportunity arising from the major building development taking place all around the theatre to obtain planning consent to extend the stage and front of house areas. This means that the full potential of the theatre can be realised with one of the best stages in the West End, ensuring it will become one of London’s most desirable and, thanks to the Victoria Station expansion scheme, strategically sited musical houses.

“With planning already approved in principle, we intend to close the theatre for about a year from late 2016, in order to tie the work into the rest of the exterior development. This purchase will take place over the next few weeks.”

He added: “The Victoria Palace and The Sondheim will bring the Delfont Mackintosh group of theatres in London up to nine continuing my desire to keep these wonderful buildings in tip-top condition for future generations of audiences and ensuring that West End theatres remain one of the key magnets for visitors to London.”

Sondheim said he was “flattered and thrilled” that the theatre would be named after him.

He said: “What I’ve always loved about London theatre is its diversity, much of which is the result of work developed in so-called fringe theatre and in non-traditional spaces.”