Here are links to a few relevant sources of information on the subject:
MigrationWatch reports that:
"For example, compared with the UK average of 22% of the working age population being economically inactive, Somali, Bangladeshi, Pakistani and Iranian immigrants are likely to be 81%, 56%, 55% and 48% economically inactive respectively"
The Daily Mail has a similar report here.
These figures come from the Institute for Public Policy report "Britain's Immigrants: an economic profile" which can be downloaded for free here.
According to the document Briefing on British Muslims: Socio-Economic Data and Attitudes:
"More than half of all Muslims are economically inactive (52 percent)."
Source
The Equalities Commission report "How Fair is Britain?", published in early 2011, contained some interesting observations about Muslim unemployment levels in the UK.
In the UK only 47% of Muslim men and 24% of Muslim women are employed.
The Wikileaks cables also contained some interesting revelations about the levels of "disability" among Muslims in Britain.
Muslims were also found to have the highest disability rates - with 24 per cent of men and 21 per cent of women claiming a disability - while the cable also cited statistics claiming Muslims were also the most likely group to be unavailable for work or not actively seeking employment due to illness, their studies or family commitments.
The original source for this information seem to have been this page on the Office of National Statistics website. It notes that "Muslim males and females in Great Britain had the highest rates of reported ill health in 2001."
Unsurprisingly, the Muslim-friendly Guardian, although at the forefront of the Wikileaks revelations, did not see fit to print this one, although the Daily Mail did.