LONDON (Reuters) - Mohammed has joined perennial favorites Jack and Joshua as one of the most popular names given to British boys in 2004, a sign of the country's growing ethnic diversity and a legacy of Muslim immigration decades ago.

The Office of National Statistics said on Thursday Mohammed -- meaning variously "one who is praiseworthy" or "exalted" -- had moved up two places to enter the top 20 for the first time.

"It is all about demographics. There are now more Muslims being born in Britain than previously," said Dr Jamil Sherif of the Muslim Council of Britain, an umbrella group of 400 organizations.

"About 40 percent of Muslims here are under 25," he told Reuters. "There are a lot of young families."

Emigration from Asia and Africa surged during the 1960s and 1970s and Britain -- population around 61 million -- is now home to about 1.6 million Muslims.

But despite its increased popularity, the name has a long way to go before it takes the laurels from Jack which has topped the charts for 10 years.

Last year, Joshua was at number two, Thomas at three, James at four and Daniel at five. Since 2000 these names have all been in the top five.

Girls' names saw more change in the top five than boys, but only marginally so.

Emily held the top spot for the second year running as did the number two name, Ellie. Jessica, the third most popular name moved up one place as did Sophie at four.

Chloe, which was top for six years until 2003, dipped to number five while Evie was the highest new entry at 39, up 22 places.

One of the fastest movers in the boys' names was Charlie, which gained nine places to 16, while last year's big climber Alfie dropped nine places to 27 and Spencer slumped 47 places.