Sinn Fein's Martin McGuinness is to make a keynote speech on British/Irish relations in London on Thursday evening.

The former IRA commander turned Northern Ireland Deputy First Minister will address a party event in Westminster following yesterday's historic meeting with the Queen during her two-day visit to Northern Ireland.

Their handshake has been hailed a watershed moment in the region's peace process and a potent symbol of reconciliation following years of violence when the IRA and British forces appeared implacable foes.

martin mcguinness

The encounter at a theatre in south Belfast would have been unthinkable a decade ago but the success of the peace process and the Queen's acclaimed visit to the Republic of Ireland last year changed minds.

Her conciliatory words in Dublin won over many critics of the monarchy and paved the way for yesterday's meeting.

The handshake was public and Mr McGuinness told the Queen in parting words of Irish: "Goodbye and God's speed."

The Mid-Ulster MP is said to have spoken to the Queen, whose cousin Lord Mountbatten was killed by the IRA in 1979, of the significance of her visit and of the need for it to be built upon in the time ahead.

Tonight's event will be attended by Sinn Fein MPs Michelle Gildernew, Pat Doherty, Conor Murphy and Paul Maskey. Sinn Fein TD for Dublin South Central, Aengus O Snodaigh, will also be in attendance.

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  • Queen Elizabeth II shakes hands with Peter Sheridan from Co-operation Ireland, left, as Prince Philip, right, meets Deputy First Minister and former IRA commander Martin McGuinness, third left, at the Lyric Theatre in Belfast Wednesday June 27, 2012. Queen Elizabeth II and a former Irish Republican Army commander offered each other the hand of peace Wednesday in a long-awaited encounter symbolizing Northern Ireland's progress in achieving reconciliation after decades of violence. (AP Photo/Paul Faith/Pool)

  • Queen Elizabeth II and Prince Philip, right, admire a gift held by Northern Ireland First Minister Peter Robinson, left, and watched by Deputy First Minister and former IRA commander Martin McGuinness at the Lyric Theatre in Belfast Wednesday June 27, 2012. Queen Elizabeth II and a former Irish Republican Army commander offered each other the hand of peace Wednesday in a long-awaited encounter symbolizing Northern Ireland's progress in achieving reconciliation after decades of violence. (AP Photo/Paul Faith/Pool)

  • Queen Elizabeth II arrives to meet Northern Ireland First Minister Peter Robinson, center, and Deputy First Minister and former IRA commander Martin McGuinness, left, at the Lyric Theatre in Belfast Wednesday June 27, 2012. Queen Elizabeth II and a former Irish Republican Army commander offered each other the hand of peace Wednesday in a long-awaited encounter symbolizing Northern Ireland's progress in achieving reconciliation after decades of violence. (AP Photo/Paul Faith/Pool)

  • Britain's Queen Elizabeth II shakes hands with Northern Ireland Deputy First Minister and former IRA commander Martin McGuinness at the Lyric Theatre in Belfast, Northern Ireland, Wednesday, June 27, 2012. (AP Photo/Paul Faith/pool)

  • Britain's Queen Elizabeth II shakes hands with Northern Ireland Deputy First Minister and former IRA commander Martin McGuinness watched by First minister Peter Robinson, centre, at the Lyric Theatre in Belfast, Northern Ireland, Wednesday, June 27, 2012. (AP Photo/Paul Faith/pool)

  • Britain's Queen Elizabeth II shakes hands with Northern Ireland Deputy First Minister and former IRA commander Martin McGuinness watched by First minister Peter Robinson, centre, at the Lyric Theatre in Belfast, Northern Ireland, Wednesday, June 27, 2012. (AP Photo/Paul Faith/pool)

  • Britain's Queen Elizabeth shakes hands with Northern Ireland's Deputy First Minister and former IRA Commander Martin McGuinness in this image taken from TV in Belfast on Wednesday July 27, 2012. The Queen is visiting Northern Ireland as part of her Diamond Jubilee celebrations. (AP Photo/TV Pool) TV OUT