The UK Statistics Authority (UKSA) has backed statisticians accused of ‘playing politics’ with immigration data.

The agencysaid the Office for National Statistics (ONS), an executive body of UKSA, was right to bring forward the publication date of the data as it was ‘consistent’ with rules on data release.

But the watchdog, which oversees the work of the ONS and any other statistics-producing public bodies, did say the office should have made a formal announcement about the change and published more supporting information.

‘On 10 February a decision was made to bring forward the publication of the news release to 11 February,’ the watchdog's statement said.

‘This decision was influenced by the level of public interest in the topic but not by other, non-statistical considerations. This is consistent with the code of practice.

‘We think that the change of date and the reasons for it should have been the subject of a formal announcement at the time the decision was made.’

The authority also said that, if the data had not been released at the time, it could have led to ‘erroneous estimates’ of the number of foreign nationals living in Britain being made, ‘as had happened in the past’.

The early release of the figures, which showed one in nine UK residents was born overseas, was criticised by immigration minister Phil Woolas as "at best, naive, or at worst, sinister".

He said the ONS needed to be "very careful" about entering "the most inflamed debate in British politics".

But the watchdog said the ONS' release had been ‘factually accurate’, with a ‘neutral and impartial’ tone.

However, to comply with the code of practice for official statistics, the release needed ‘more supporting information, to enable the reader better to understand the estimates, the context in which they are produced and their strengths and weaknesses’.

‘In this respect we recommend that future such releases should contain both further explanation and further references to supporting documents, in order to meet the expectations of the code.’

The authority also said the release should have mentioned that the figures had ‘some weaknesses’ when used to measure trends in migrant workers.

UKSA chairman Sir Michael Scholar dismissed Woolas' criticism of the ONS at the time of the row. ‘Whether you call it naivety or openness, statisticians must be encouraged to publish independent and objective statistics, not pilloried for doing so,’ he wrote.

In a statement on Monday, he added: "I have already rejected any suggestion of political motivation in the steps ONS took.

"The national statistician exercised her professional judgment in deciding to bring forward the release of the regular analysis of these statistics of the country of birth and nationality of workers, both because there has been misinterpretation of these figures in the past and because she judged that it was in the public interest to publish neutral and objective statistics on this subject as soon as possible, given that the underlying data-set was widely available.

"The statistics authority will ask ONS to ensure that the lessons from the assessment we have published today are agreed and accepted.

"We will continue to support and defend the freedom of professional judgment of the national statistician."