LONDON, Jan. 6 (Reuters) – Muhammad joined the perennial favorites Jack and Joshua in 2004 as one of the most popular names given to British boys, a sign of growing ethnic diversity and a legacy of Muslim immigration decades ago. The Office of National Statistics said Thursday that Muhammad, meaning “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,” said Dr. Jamil Sherif, of the Muslim Council of Britain, an umbrella group of 400 organizations. “There are now more Muslims being born in Britain than previously. About 40 percent of Muslims here are under 25; there are a lot of young families.” Immigration from Asia and Africa surged during the 1960’s and 70’s and Britain, with about 61 million people, is home to about 1.6 million Muslims. But despite its increased popularity, Muhammad has a long way to go before it takes the laurels from Jack, which has topped the charts for 10 years. Joshua was No. 2, Thomas at 3, James at 4 and Daniel at 5. For girls, Emily held the top spot for the second year running, and Ellie was again No. 2.