Already anointed by royalty for his services to music, Sir Paul McCartney has been honoured by the Master of the Queen's Music, Sir Peter Maxwell Davies, the Orcadian composer who has dedicated his latest composition to the former Beatle.

Sir Peter, 74, has written Liber Pulsationis Fabulatoris, a 20-minute choral work which will be performed at Liverpool's Metropolitan Cathedral next month. The title means “The Book of Pulsations of the Creator of Legends” and Sir Peter explained that the first three letters spell “lib pul fab”, an echo of the band at the height of the 1960s fame, albeit in Latin.

The work is a setting of Hildegard of Bingen, a 12th-century German poet and has been commissioned as part of the celebrations for Liverpool 2008 European Capital of Culture.

In June, Sir Peter attended his first pop concert in Liverpool after a personal invitation from Sir Paul, 66, who told him to bring earplugs to his performance at Anfield Stadium. In return Sir Paul, who is said to be “thrilled to bits” by Sir Peter's new composition, has been invited to its premiere.

“Paul is as great as Schubert and still has not received the full recognition that his talent deserves. This country has produced one of the greatest musical talents ever and we should appreciate and celebrate that loudly,” said Sir Peter, who selected Yesterday by the Beatles among his eight records when he appeared on the radio show, Desert Island Discs in 2005. Sir Peter's extravagant praise carries echoes of William Mann, the Times classical music critic, who stunned the music world when he named the Beatles “the outstanding English composers of 1963” and later compared the Sgt. Pepper album to the work of Monteverdi, Schumann and Britten. Almost all of the Beatles songs were written by Sir Paul and the late John Lennon.

Since his 1960s heyday, Sir Paul's work has struggled to win such levels of acclaim, with rock critics ridiculing releases such as The Frog Chorus, Mull of Kintyre and Mary Had a Little Lamb. Coincidentally, some classical music critics believe that Sir Peter's own work has lost its edge since the days when it was praised for its “ungrammatical attitude to tonality” by Mann - a quality it shared, he said, with the work of the Beatles.

In recent years, Sir Paul himself has turned to classical composition, but the four albums he has released have not always fared well with critics. His first classical piece, Paul McCartney's Liverpool Oratorio, was composed for the Royal Liverpool Philharmonic Society's 150th anniversary in 1991, and received a grand premiere in the city's Anglican cathedral - where Sir Paul was rejected as chorister as a boy.

The work was much derided by critics, who lamented his abandonment of any rock elements. Sir Paul's most recent oratorio Ecco Cor Meum (Behold my heart) won him a Brit Award but was reviewed in The Times as “banal” and “depressingly feeble”.

It is a long way from Mann's praise for the pop output, which “have brought a distinctive and exhilarating flavour into a genre of music that was in danger of ceasing to be music at all”.

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