A Norfolk MP yesterday told the Leveson Inquiry that a News International lobbyist suggested Rupert Murdoch's newspapers would 'turn nasty' with the Liberal Democrats if they did not approve the firm's bid to takeover BSkyB.

At the time the alleged threat was made, Lib Dem business secretary Vince Cable was in charge of giving government approval to the takeover.

Since then both Mr Cable and Lib Dem leader Nick Clegg have alluded to the incident while giving evidence at the inquiry into press ethics.

In particular, Mr Clegg recently told how the alleged threat was first made to Mr Lamb, his main advisor at the time, before being reported back to him later on.

Mr Lamb said in oral evidence at the inquiry yesterday that he had met lobbyist Fred Michel twice, on June 10 and October 27 2010, and that the threat was made at the second meeting.

Explaining why he had come to give evidence at the inquiry, Mr Lamb said: 'When Vince Cable gave his evidence I felt I had to tell the story of what happened.'

During the hearing Mr Lamb produced a note that he had written shortly after the October meeting with Mr Michel. It described the encounter as 'extraordinary', Mr Michel as 'very charming' and the lobbyist's attitude as 'brazen'.

He wrote in the note that Mr Michel had said he wanted the decision-making process around the takeover bid to run smoothly, adding that if it went 'the wrong way', by referring the bid to the media watchdog Ofcom for example, then the implications might be worrying.

The note said: 'It was brazen. VC [Mr Cable] refers bid to Ofcom, they turn nasty.'

However, Mr Lamb also told the inquiry that Mr Michel indicated that if Mr Cable allowed the takeover bid to proceed then the News International flagship paper, The Sun, could help promote the introduction of the alternative vote electoral system.

The voting reform was a key Lib Dem policy until it was defeated at a national referendum in 2011.

The Norfolk MP told the inquiry that having left the meeting with Mr Michel he had 'a very clear understanding' that News International titles had been helpful to the party before, but could easily change their allegiance.

At the end of the hearing a lawyer for Mr Michel stood up and denied that his client had made any threat in the meeting with Mr Lamb.