Christmas should be downgraded in favour of festivals from other religions to improve race relations, says an explosive report.
Labour's favourite think-tank says that because it would be hard to "expunge" Christmas from the national calendar, 'even-handedness' means public organisations must start giving other religions equal footing.
The leaked findings of its investigation into identity, citizenship and community cohesion also propose:
• "Birth ceremonies", at which state and parents agree to "work in partnership" to bring up children
• Action to "ensure access" for ethnic minorities to "largely white" countryside
• An overhaul of Britain's "imperial" honours system
• Bishops being thrown out of the House of Lords
• An end to "sectarian" religious education
• Flying flags other than the Union Jack.
The report by the Institute for Public Policy Research was commissioned when Nick Pearce, now head of public policy at Downing Street, was its director.
IPPR has shaped many Labour policies, including ID cards, bin taxes and road pricing.
The report robustly defends multiculturalism - the idea that different communities should not be forced to integrate but should be allowed to maintain their own culture and identities.
And it says immigrants should be required to acquire some proficiency in English and other aspects of British culture "if - but only if - the settled population is willing to open up national institutions and practices to newcomers and give a more inclusive cast to national narratives and symbols".
It adds: "Even-handedness dictates that we provide public recognition to minority cultures and traditions.
"If we are going to continue as a nation to mark Christmas - and it would be very hard to expunge it from our national life even if we wanted to - then public organisations should mark other religious festivals too.
"We can no longer define ourselves as a Christian nation, nor an especially religious one in any sense.
"The empire is gone, church attendance is at historically low levels, and the Second World War is inexorably slipping from memory."
The report, written by IPPR advisers Ben Rogers and Rick Muir, calls on Ministers to launch an "urgent and upfront campaign" promoting a "multicultural understanding of Britishness".
"Multiculturalism can be shown to provide for a fairer and more liberal society and does not necessarily lead to social division and community conflict, as its critics have claimed," it says.
Councils must act to "ensure children mix and are able to form friendships with pupils from different backgrounds".
The report adds: "Any liberal state should recast the civic oaths and national ceremonies, or institutions like Parliament and the monarchy, in a more multi-religious or secular form and make religious education less sectarian."
The presence of bishops in the House of Lords, for instance, is condemned as an "anachronism" that should be removed.
The system in which parents are required to register a new baby at a register office is dismissed as "purely bureaucratic".
The occasion should be transformed into a "public rite", using citizenship ceremonies for immigrants as a model, the report says.
"Parents, their friends and family and the state [would] agree to work in partnership to support and bring up their child."
Rural Britain, the report complains, "remains a largely white place".
Much more needs to be done to "ensure access" to the countryside for black and ethnic minority groups, disabled people and children from inner-city areas.
Sayeeda Warsi, the Conservative spokesman on community cohesion, said: "Their comments betray a breathtaking misunderstanding of what it is to be British. These proposals could actually damage cohesion."
She added: "You don't build community cohesion by throwing out our history and denying the fundamental contribution Christianity has played and does play to our nation.
"As a British Muslim I can see that - so why others can't just staggers me."
And she attacked ceremonies to mark the registration of a baby.
"The thought of Gordon Brown sharing responsibility with me for bringing up my children sends a shiver down my spine. I thought we got rid of communism?"
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