An MP accused of an undeclared lunch with a lobbyist behind controversial plans to build a rail freight depot near Park Street has been cleared of wrongdoing.

The Downing Street inquiry into allegations against Cabinet minister Theresa Villiers- now Northern Ireland Secretary has been denounced as a "complete and utter whitewash" by St Albans MP Anne Main.

Mrs Main complained to Number 10 in September after learning that Ms Villiers met with Simon Hoare, a chief lobbyist for developer Helioslough and former university friend, in August 2011, weeks before the Secretary of State for Communities and Local Government was due to reassess plans for a major rail freight on the former Radlett Aerodrome site.

In a letter to Mrs Main, Cabinet Secretary Sir Jeremy Heywood said that “there was no evidence that Ms Villiers sought to intervene improperly, in the planning appeal process.

Before saying that Ms Villiers 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."

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' behaviour 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".

She said: “My constituents could be forgiven for thinking this was a white wash. This enquiry took four months; never has it taken so long to say so little.

“I do not believe Sir Jeremy Heywood has addressed my specific allegation concerning 7.1 of the Ministerial Code which states that: “Ministers must ensure that no conflict arises, or could reasonably be perceived to arise between their public duties and their private interests, financial or otherwise.

“If this is the answer then it appears to be acceptable that ministers can have private undeclared lunches with old friends to discuss sub judice planning decisions with impunity.

“This does not feel like justice for my constituents, we still hope that this decision will be overturned but in the mean time I still believe there are serious unanswered questions surrounding the transparency of the decision making for this application. “