IT'S a mystery that would perplex even Inspector Morse - how have two decades gone by so quickly since the first time the wily detective appeared on our screens?

Inspector Morse is 20 - and a special weekend is planned later this month climaxing with Morse At The Royal Albert Hall.

It will be an evening of music, hosted by Michael Parkinson and opera stars Lesley Garrett, Sir Willard White and Alfie Boe.

The Albert Hall concert will include performances of music specially selected from the popular series. It will feature music from composers, including Wagner, Mozart, Puccini, Handel and Haydn.

It will be held on Thursday, April 19, and transmitted on ITV3 during the Morse weekend on April 28 and 29.

Oxford-based Morse author Colin Dexter said: "I'm looking forward to the night at the Albert Hall. Music always played a big part in Morse's life, especially Wagner, who was his great musical hero, and mine.

"My musical tastes have always centred upon the latter half of the 19th century."

The London Philharmonic Orchestra will be joined on stage by the Crouch End Festival Chorus, conducted by Simon Wright.

Award-winning composer Barrington Pheloung, who created the famous Morse theme and original music for the series, will also make a guest appearance on the conductor's podium.

Kevin Whately, who played Morse's long-suffering colleague in the series, and now stars in the new ITV drama Lewis, will also make a special appearance in the TV programme.

ITV3's Inspector Morse Weekend will also feature new documentaries, including There's Something About Morse, in which actors - among them John Thaw's widow Sheila Hancock - writers and producers explore the success of the ITV series.

The Music of Morse, a detailed examination of how music is used in the drama narrated by Kevin Whately, will also feature.

The channel will also screen 12 Morse episodes, each with an introduction by Kevin as he recounts his memories from filming, including his first encounter with John Thaw and their trip to Australia for The Promised Land episode.

The Morse episode which shows how the Oxford detective made the transition from page to screen will also be screened as part of the weekend.

There will be another chance to see The John Thaw Story, first transmitted on ITV in 2002, the year of John's death at the age of 60.

Steven Andrew, programme director at ITV Digital Channels, said: "Celebrating the 20th anniversary with a weekend dedicated to Inspector Morse is a fitting way to acknowledge Morse's important contribution to our television culture."

Classic FM managing director Darren Henley said: "Inspector Morse is one of TV's great icons and a character whose name is synonymous with classical music."

Inspector Morse has attracted some of the largest drama audiences on British television since it was first seen in January 1987.

It has always been a magnet for the cream of British acting talent in its guest roles, with suspects and villains, academics and victims being played by the likes of the late Sir John Gielgud, Richard Briers, Anna Massey, Richard Wilson, Frances Barber, Joanna David, Sean Bean, Jim Broadbent and Diana Quick.

Early appearances in Morse saw actors such as Amanda Burton, Philip Middlemiss, Martin Clunes and Charlotte Coleman, while a young Elizabeth Hurley appears in Last Seen Wearing as a pupil at a girls' private school.

Behind the camera in the leafy streets and college quadrangles of Oxford have been future Oscar winners like Shakespeare In Love director John Madden and Trainspotting's Danny Boyle.

The English Patient director Anthony Minghella wrote the first Morse screenplay, for The Dead Of Jericho and two further screenplays.

The Dead Of Jericho established the format of two-hour drama on television, after executive producer Ted Childs and the first producer, the late Kenny McBain, brought the creation of former classics master Colin Dexter to the small screen.

Inspector Morse has had a global audience of a billion people in 200 countries, ranging from Canada to Mongolia, Malawi to Nepal, El Salvador to Papua New Guinea. In 1990, John Thaw received the BAFTA Award for Best Actor for his portrayal of Morse, and the next year was voted ITV Personality of 1990 and TV Times' Favourite Actor of 1990. Other awards have been bestowed on composer Barrington Pheloung and the team of writers on the fifth series.