The third runway at Heathrow will be built in 2015 under the expansion plan
The Department for Transport (DfT) is facing an "intensive investigation" over claims e-mails about the expansion of Heathrow Airport were deleted.
The exchanges with airport operator BAA were requested by a Conservative MP under the Freedom Of Information Act, who said she then spotted gaps.
The Information Commissioner's Office (ICO) confirmed it would examine the 2007 e-mails about the third runway.
The DfT said all freedom of information cases had been handled "responsibly".
Justine Greening, Tory MP for Putney in south-west London, said she asked for the investigation after noticing gaps in e-mail conversations between September and November 2007.
"There were a variety of e-mails on important issues that never had an end. I think it seems very unlikely there was that level of e-mail conversation where there was never an end," she told the BBC.
"And it was unlikely that they were sporadically deleted in a random way... it was the end of conversations that were never resolved," she said.
Ms Greening said she made three identical requests under the Freedom Of Information (FOI) Act, in July 2006, September 2007 and April 2008.
The Conservative shadow local government minister said she wanted to find out what discussions were going on within the DfT in the run up to the consultation on Heathrow's expansion.
"I'm very pleased the Information Commissioner's Office (ICO) is investigating, it's important one way or another to find out what has happened," she said.
"I very much hope, if e-mails were withheld, that those are then made public."
She said the ICO had told her it planned "quite an intensive investigation in a short timescale with the limited resources available to our office".
Ms Greening, who has campaigned against the £9bn expansion, said millions of Londoners had had their lives ruined by overhead flights and air pollution from Heathrow.
"Until ministers reverse their decision to expand the airport, we will continue to campaign," she said.
Last year the Conservatives pledged to scrap plans for a third Heathrow runway if elected.
A DfT spokesman said: "We are aware of a possible investigation by the Information Commissioner's Office, but have not received any formal notice.
"The department has received a number of FOI cases in relation to expansion at Heathrow, and we believe they have all been handled responsibly and in accordance with the Act."
The ICO said: "We are looking into allegations made by Justine Greening MP concerning requests for information to the Department for Transport.
"We have contacted BAA and the DfT to help us establish the full facts."
It is a criminal offence to delete or conceal records to prevent them from being disclosed under the Freedom of Information Act.
A BAA spokesperson said the company was not covered by the FOI Act and did not have any comment to make.