The UK Statistics Authority is looking into whether David Cameron broke the law by hinting that the GDP figures due to be released tomorrow would show the British economy had grown.
Under pressure from Ed Miliband at prime minister's questions, Cameron sought to emphasise recent positive indicators on the economy and said: "I can tell you, the good news will keep coming."
The prime minister is one of a very small group of people who are given advance 24-hours notice of the market sensitive data.
Under the rules of the the Pre-release Access to Official Statistics Order 2008 the information is not supposed to be made public early.
Asked whether the prime minister had broken the rules, the UK Statistics Authority told the Huffington Post UK: "we're looking into it".
The Labour Party said Cameron had "let slip" that the figures would show Britain had emerged from recession, but Cameron's official spokesman denied that the prime minister was talking about the GDP figures specifically.
Anticipating that the figures will bring good news, shadow chief secretary to the Treasury, Rachel Reeves, said they were skewed by the Olympic Games and bank holidays.
“The prime minister seems to have let slip what we already knew – that the Olympics will help Britain finally emerge from the longest double-dip recession since the Second World War," she said.
“The question is what the underlying growth rate of the economy is when we strip out the one-off Olympics and Bank Holiday effects.
She added: “Growth of one per cent would simply mean the economy is the same size as a year ago. A one-off boost from the Olympics is no substitute for a long-term strategy and should not breed yet more complacency from David Cameron and George Osborne.”