The Home Office has been "highly selective" in its use of drugs seizure figures "in order, it seems, to show the UK Border Agency in a good light", the chairman of the UK Statistics Authority has said.
Sir Michael Scholar wrote to Home Office Minister Damian Green seeking reassurances that suggestions the move 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 unfounded.
The publication of the figures last week was "irregular and inconsistent" with the code of practice and the Ministerial Code and should not happen again, Sir Michael said.
The UK Border Agency released figures on November 4, for publication last Monday, showing that border officials seized more cocaine and almost double the amount of heroin in the last six months than in the whole of the previous year. But just three days later, the official Home Office Statistical Bulletin showed the amount of cocaine seized by border officials in England and Wales had actually fallen by a quarter in 2010/11 compared with 2009/10, and the amount of heroin seized had halved.
In his letter to Mr Green, Sir Michael wrote: "The Statistical Bulletin makes reference to a fall in the volume of seizures of class A drugs in the most recent period. This contrasts with the November 4 press release, which highlights a large increase in seizures, albeit for a different time period.
"The November 4 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 any involvement by, and 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 went on: "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. I would welcome your reassurance that this is not the case. Were it to be the case, the authority's view is that this would be highly corrosive and damaging to public confidence in official statistics."
UKBA chief executive Rob Whiteman welcomed the initial figures, saying: "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."
Mr Green said that "stopping harmful drugs like heroin and cocaine means we're helping keep communities safe and preventing criminals exploiting the UK".