Another fine mess for the Home Secretary

Home Office ministers faced a fresh crisis last night after being rebuked for manipulating drug-seizure figures in an apparent attempt to generate good publicity for the embattled Border Agency. Sir Michael Scholar, the chairman of the UK Statistics Authority, condemned the department for a "highly selective" briefing to journalists which claimed that the amount of heroin and cocaine detected at ports and airports had soared – just days before properly audited figures showed seizures had fallen.

The row comes as Theresa May, the Home Secretary, faces a public battle with the former head of the border force, Brodie Clark, who has accused her of destroying his reputation.

The Cabinet Secretary, Sir Gus O'Donnell, has been asked to examine whether staff acting for Ms May briefed newspapers against Mr Clark. Sir Michael made his rare intervention after crime reporters were told that more cocaine and almost double the amount of heroin were detected between April and September of this year than in the whole of the previous 12 months. They held the briefing on 4 November for publication three days later.

But the department's official Statistical Bulletin showed the amount of heroin seized in England and Wales had actually halved in 2010-11 compared with 2009-10, while the amount of cocaine found was down by one-quarter.

Sir Michael warned that the publication of the figures broke Whitehall rules on the handling of statistics and ran counter to the ministerial code. He wrote in a letter to Damian Green, the Immigration minister: "The 4 November press release, which appears not to have been published on either the Home Office or the UK Border Agency websites, and seems to have been distributed only to a select group of journalists, makes no reference to the forthcoming Statistical Bulletin.

"It was, I understand, produced without the knowledge of the department's statisticians and it is highly selective in its choice of statistics, in order, it seems, to show the UK Border Agency in a good light."

He added: "It has been suggested to me that one motivation for this release was to generate positive news coverage ahead of the release of the National Statistics which showed a decline in the volume of drug seizures. Were it to be the case ... this would be highly corrosive and damaging to public confidence in official statistics."

The briefing on the initial figures was accompanied by a comment from Mr Green, who said: "Stopping harmful drugs like heroin and cocaine means we're helping keep communities safe and preventing criminals exploiting the UK."

A quote was also supplied from the UKBA chief executive, Rob Whiteman, who said: "Our work to secure the border all day, every day, continues to show significant results despite the efforts of organised crime gangs to circumvent our controls."

The UKBA described the statistics as "management information" rather than fully audited figures and stood by the decision to release them.

A spokesman said: "The figures used to highlight the UK Border Agency's work in tackling the harm caused to communities by cocaine and heroin were clearly labelled management information. We take our responsibilities under the statistics code seriously and are promptly responding to Sir Michael Scholar."

But Yvette Cooper, the shadow Home Secretary, called for an investigation by Sir Gus O'Donnell into whether either Ms May or Mr Green had broken the ministerial code. She said: "Sir Michael's letter brings into question the 'highly selective' use of statistics by ministers."