Published Friday, 29 June 2012
US President Barack Obama on the phone in the Oval Office at the White House. (© Getty)
Fresh from his historic meeting with the Queen, Mr McGuinness said he thought people would be shocked by what he called Mr Cameron's "lack of engagement".
The comments were made during a speech at the House of Commons in London on Thursday evening.
Since the Hillsborough Agreement, the Northern Ireland leaders have had to first raise any issues with Secretary of State Owen Paterson instead of going directly to the prime minister.
But Mr McGuinness accused the British government of having made "very wrong and unhelpful decisions" - referring to issues including the detention of republican prisoners Marian Price and Martin Corey.
There are issues that have not been brought to a conclusion, specifically the issue of the legacy of the conflict - the British Government has a big role to play in that.
He added: "This lack of engagement by David Cameron is a serious mistake and may provide a rational for some of the damaging decisions made by Owen Paterson during his tenure at the NIO."
Addressing the Northern Ireland Assembly in June last year, Mr Cameron stressed that his commitment to Northern Ireland was "heartfelt and sincere".
"I am passionate about this part of the United Kingdom, deeply mindful of history, and deeply determined to work with you towards a better future," he said.
But it was the first time the prime minister had visited Northern Ireland in more than a year.
When challenged, he insisted: "I did make, before the election, some promises to people in Northern Ireland and I hope people will judge me on those promises - not just on how often I set foot here."
Mr McGuinness and his DUP counterpart Peter Robinson have travelled to London to meet with Mr Cameron at Downing Street on occasion.
However, the deputy First Minister is convinced their trade missions to the US have granted them more access to arguably the world's most powerful man, Barack Obama.
The president has also met with Mr McGuinness and Mr Robinson in Dublin last year, where he praised the progress made in Northern Ireland and vowed: "America will stand by you always in your pursuit of peace."
In his House of Commons address on Thursday, Mr McGuinness said that it was time for a new approach to British-Irish relations and that challenges lay ahead for everyone.
"We will need new thinking. We will need new ideas. We will need new political realities to dawn," he said.
"That will not happen if the British Government continues to cling to old certainties, born from a different era and a different time."