Existing methods of estimating migration and population figures are not "fit for purpose" say MPs.
The International Passenger Survey, designed to provide data for tourism, now plays a central role in migration estimates, the committee of MPs said.
They said it was "not fit for this purpose" and methods of measuring movement in the UK "unsatisfactory".
The committee said new surveys were needed. The Lib Dems said ministers had "totally lost track" of the population.
In its Counting the Population report, the Commons Treasury Committee accepted that the UK was in a period of "significant population change" which made it harder to estimate numbers of people in each area.

But it said population estimates were "central to every national system of official statistics", used to estimate funding for local government, the NHS and other public services.
Getting them right was therefore "a matter of social responsibility" the report said.

Sub-committee chairman, the Conservative MP Michael Fallon, said they heard evidence that councils including Westminster, Slough and Manchester had been given reduced funding, because of "inaccurate statistical data".
"It is now impossible to estimate accurately the UK population today. Unreliable statistics make planning impossible. We call on the government to improve the population count as a matter of urgency. "

For the Lib Dems, Chris Huhne said: "This report makes it painfully clear that ministers have totally lost track of something as fundamental as how many people actually live in Britain."

BBC NEWS | Politics | MPs attack migrant count methods

How many are here ? ...... Answer no idea !

'Not Fit for Purpose' sums this Government up perfectly , role on the General Election.