Yusuf Islam's name appeared on a US terrorism "watch list" last month

Islam, who recently hit the headlines after being refused entry to the US, has not released a single for 30 years.

But the pair have now recorded a version of his 1970 song Father and Son, which was a hit for Keating's former band Boyzone in 1995.

It is 6/1 with William Hill to be the UK's top-selling Christmas single.

Their nearest rivals, according to the bookmaker, are U2 and Robbie Williams, both at 12/1.

CHRISTMAS NUMBER ONE ODDS 6/1 - Ronan Keating (above) and Cat Stevens 12/1 - U2 12/1 - Robbie Williams 14/1 - Kylie Minogue Source: William Hill

A spokesperson for Keating said the pair met after Islam took his son to see Boyzone perform his song on Top of the Pops.

"They got on really well and just stayed in touch over the years," she said.

"They were chatting one day, Ronan gave him a call, and it came up in conversation. He asked him if he'd be interested in doing it."

The duet marks the culmination of a quiet comeback to the music scene for Islam.

After having hits with songs like Moon Shadow, Peace Train and Morning Has Broken, he converted to Islam in 1977 and distanced himself from his past career.

But in 2003, he re-recorded Peace Train as an anti-war message, although it was only available for download.

And later that year, he played a rare concert at London's Royal Albert Hall.

But this September, he was barred entry to the US on "security grounds" after his name appeared on a terrorism "watch list". Islam, 56, denies supporting terrorism.