Chipping Barnet MP Theresa Villiers has been cleared of wrongdoing over an undeclared lunch with an influential lobbyist and former university friend while she was transport minister.

Ms Villiers - now Northern Ireland Secretary - met Simon Hoare, a chief lobbyist for developer Helioslough, in August 2011, weeks before the secretary of state for communities and local government was due to reassess plans submitted by Helioslough for a major rail freight depot in St Albans.

In September this year, St Albans MP Anne Main wrote to Cabinet Secretary Sir Jeremy Haywood asking for an investigation into whether or not Ms Villiers’ failure to declare the potential conflict of interest amounted to a breach of the ministerial code".

But in a letter to Mrs Main, he said that "there was no evidence that the Conservative politician sought to intervene improperly, in the planning appeal process".

Before saying that, the Conservative politician had reassured him "this was a personal engagement with a longstanding friend".

He said: "This is a position that has been supported by accounts from both departments and I have absolutely no reason to doubt these accounts.

"Having considered this matter in full, I believe that both departments acted properly in respect of the planning appeal and that there is no evidence that decisions were affected by lobbying on behalf of Helioslough or other parties."

The findings have been denounced as a "complete and utter whitewash" by Mrs Main.

In a statement released by her office, Mrs Main said she was "very angry and deeply disappointed by the scant response" because Sir Jeremy had failed to address the provision in the code governing ministers' behavior, which requires them not only to avoid conflicts of interest between their public duties and private interests, but also to ensure that no such conflict "could reasonably be perceived to arise".

A spokesman for Ms Villiers said: "Mrs Main's complaint has been investigated by the Cabinet Secretary, Sir Jeremy Heywood, who concluded that there was no improper interference with the planning process and no breach of the Ministerial Code."

"Any rail minister, as Theresa Villiers then was, will have matters relating to rail raised with them from time to time in all sorts of settings. The conversation with Mr Hoare was disclosed to parliament. No action was taken as a result of that conversation and nothing from it was passed on to the minister with responsibility for the decision on the Radlett planning application or to any other ministerial colleagues.

"It, therefore, had no impact on the planning process. Theresa Villiers has never been the minister responsible for taking the decision on the Radlett planning application."