President Mary McAleese has described the State visit of Britain's Queen Elizabeth as an extraordinary moment in Irish history.

In an RTÉ interview, the President also says this is 'absolutely the right moment' to welcome the head of state of our nearest neighbour onto Irish soil.

'I think it is an extraordinary moment in Irish history, a phenomenal sign and signal of the success of the peace process and absolutely the right moment for us to welcome onto Irish soil.

'Her Majesty, the Queen, the Head of State of our immediate next door neighbours, the people with whom we are forging a new future, a future very, very different from the past, on very different terms from the past and I think that visit will send the message that we are, both jurisdictions, determined to make the future a much, much better place.'

British Prime Minister David Cameron has told RTÉ News that the four-day visit will be a huge step forward.

Meanwhile, parking restrictions are in place across the capital ahead of the Queen's arrival tomorrow.

Some roads are already closed in Dublin and barriers are lining many routes.

Gardaí say it is the biggest security operation the force has ever undertaken, with up to 8,000 members of the force involved.

The National Roads Authority has said it will lift tolls on the Port Tunnel if traffic congestion becomes a problem.

Gardaí are assisting Dublin City Council on its information service advising people who need to access the city in the coming days.

There will be localised restrictions at several locations in Dublin city.

Roads though the Phoenix Park remain open, but no parking is allowed there until later this week.

A 100km restriction is in place on the M8 motorway close to Cashel, Co Tipperary, and traffic has been reduced to one lane there.

The most significant disruption will be tomorrow, when the north and south quays and the N4 into Dublin city will be closed for several hours.

Dublin City Council's Michael Phillips says contingency plans are in place.

Commuters are being urged to use public transport if possible.

However, Dublin Bus, Bus Eireann, DART and the Luas will all be subject to diversions and delays and a number of the Dublin Bikes stations will be closed.

Gardaí say they will do everything they can to accommodate onlookers, but that they will be kept at a distance.

Garda Commissioner Martin Callinan has thanked the public for their assistance in the security operation.

Meanwhile, Irish Republican dissidents have issued a bomb threat for central London, Scotland Yard said today.

Open letter to Queen from Justice for the Forgotten

Survivors and bereaved relatives of the victims of the Dublin and Monaghan bombings have written an open letter to Queen Elizabeth.

Her arrival tomorrow coincides with the 37th anniversary of the attacks in which 34 people, including an unborn baby, were killed - the greatest loss of life in a single day of the Troubles.

The 'Justice for the Forgotten' group wants the Queen to urge Britain's Prime Minister to release files that were withheld during the inquiry into the bombings.

The appeal comes as the Dáil prepares to debate a Sinn Féin motion calling on the British government to release all files relating to the bombings.

Meanwhile, the Peace and Neutrality Alliance group has said the visit by the British Queen is not the establishment of a 'new relationship', but the re-establishment of an old one.

In a statement, PANA said that while President McAleese described the visit as the culmination of the Irish Peace Process and the establishment of a 'new relationship' with England, they see it otherwise.