Opposition parties last night accused the government of trying to "bury bad news" behind the camouflage of Tony Blair's big announcement by releasing new figures on the rising cost of ID cards and making public the loss of almost 400 civil service jobs, including scores in Edinburgh.

MPs heard the projected cost of the controversial identity card scheme had risen by at least £400m in just six months. However, Conservatives and Liberal Democrats claimed, when expressed in 2007-08 prices, the true rise was £640m, producing a total of £5.6bn over 10 years.

The Home Office was accused of breaking the law by publishing its compulsory twice-yearly update on ID cards more than one month late, coinciding with the Prime Minister's setpiece statement.

"The public will see through this transparent and pathetic attempt to bury bad news," declared David Davis, Shadow Home Secretary, warning the public to brace itself for further rises in ID card costs every time the estimate was updated.

Nick Clegg, for the Liberal Democrats, said: "It is bad enough that the government seeks to bury bad news behind the camouflage of Tony Blair's announcement. Breaking the law to do so breaks new ground even for Tony Blair's Labour Party."

He argued the "illegally postponed" bad news on ID cards showed the depths of cynicism and media manipulation to which ministers were now resorting to "ram this increasingly unpopular scheme through".

The figures showed the costs over 10 years were estimated to be £5.3bn from 2006 to 2016 compared with £4.9bn in the last calculation. A further, separate estimate said the scheme would cost £5.6bn over the10 years from 2007 to 2017.

The Home Office also published a further estimate of £200m over 10 years to introduce biometric identity documents on non-Europeans who apply to extend their leave to stay in the UK.

Shami Chakrabarti, director of civil rights group Liberty, said: "The soaring costs and declining support for the grand ID card folly are increasingly inescapable. Surely, this dangerous and expensive idea must leave No 10 with its author."

Last night, the Home Office said April 9, when the new ID costs were expected to be released, had fallen during Westminster's Easter holiday and the department had released the figures "as soon as we possibly could".

The timing with Mr Blair's departure announcement was coincidental, a spokeswoman insisted.

Separately, the Department for Work and Pensions, the government's largest, was also accused of burying bad news over the announced closure of three offices, including one in Edinburgh, with the loss of a total of 380 jobs.

"It is scandalous that this announcement has been slipped out when all eyes are on the departure of Tony Blair," said Mark Serwotka, general secretary of the Public and Commercial Services Union.

However, a spokesman for the DWP said: "We are doing everything we can to find suitable redeployment opportunities for members of staff, either within local DWP sites or with other government departments."