Should Ireland rejoin the Commonwealth, both in its own interests and as a contribution to the peace process by reassuring Northern and Southern Protestants?

Mainstream and influential opinion-formers have at last begun to discuss the once-heretical proposition that 50 years after it quit in anger, the Republic could rejoin in friendship.

The former President, Mrs Mary Robinson, floated the issue last year. She said the answers would say much about Irish insecurity and identity.

Undoubtedly and understandably, many Irish people instinctively mistrust and dismiss the Commonwealth, historically associated with the British empire's previous power and pomp.

But times have changed. The Commonwealth cannot in any way be described as Britain's stooge but has developed into a very different institution since the Republic of Ireland left in 1948.

The Commonwealth has been reshaped by those countries which struggled for freedom from colonialism and now value their independence.

At worst, it might be a talking shop. But it mostly provides a forum for a unique international dialogue that often pays dividends and costs little.

The Commonwealth is a free association of 54 sovereign states. It is a rich mosaic of the modern world.

The Commonwealth combines black and white, Catholic, Protestant and dissenter, Muslim, left and right, east and west, north and south, rich and poor as well as a range of political systems. From Antigua to Zimbabwe, Jamaica to South Africa, Cyprus to Pakistan, the Commonwealth has a foot in every continent.

They nearly all have a shared relationship with Britain. This is not the case with countries such as Mozambique and the Cameroons. Other such countries are possible candidates, including Palestine, Angola, Rwanda, Eritrea and Yemen. No one can deny the diversity of the modern Commonwealth.

The Commonwealth is probably best known for its athletic games. But it also aims to promote democracy, economic development and international understanding.

The Commonwealth also embraces progressive actions. Against Mrs Thatcher's advice, it took a leading role in helping to isolate apartheid. One of Nelson Mandela's first acts on becoming South African President was to rejoin the Commonwealth.

The Commonwealth contains republics and countries with their own monarchies. Queen Elizabeth is head of state in 16 countries, while five countries with their own monarchies and 33 republics don't give her any constitutional recognition. However, they all recognise her as a symbol of their free association and she is head of the Commonwealth.

Rejoining the Commonwealth could connect the Republic to a wide range of friendly countries around the world, increase its diplomatic punch and possibly boost trading opportunities, without surrendering any republican principles or compromising Irish independence in any way.

An application for membership would probably meet with a very positive response from Commonwealth governments.

But there may be another big benefit of rejoining. It could greatly reassure Northern unionists who fear that their British identity is ignored in the Republic and might be further ignored as the two parts of the island draw together.

British-Irish relations are full of apparent paradoxes. Northern Ireland's Troubles have claimed proportionately more lives than any other such conflict in western Europe but without increasing enmity between Ireland and Britain. In fact, our two countries have grown closer.

The peoples of these islands are enmeshed in a massive web of personal, cultural, social, economic and human relationships. We watch the same football teams and television programmes and read many of the same papers. There are more Irish people in Britain than in the Republic. The extent of mingling is very high.

But the two main communities in Northern Ireland are not fully part of this modern success story. The nightmare of many Northern nationalists is that they will be abandoned by the South. The nightmare of Northern unionists is that they will be sold out by Britain. The all-important Trimble-Mallon political axis is the way of assuaging such fears.

North-South bodies are also politically important to persuading Northern Catholics that they will never again be second-class citizens.

But unionists also need reassuring. Ireland rejoining the multicultural Commonwealth could come to symbolise the South's understanding of British identities in both parts of Ireland.

It would also encourage efforts to deepen official and popular links between east and west, Dublin and London, which is an often understated part of the Belfast Agreement overwhelmingly ratified by the peoples of Ireland, North and South.

Ireland rejoining the Commonwealth is no longer a quack idea and isn't any sort of quick fix. But better relations between London and Dublin including within the Commonwealth, building on the common British-Irish heritage, could simultaneously advance the Irish State's diplomatic and economic interests and give comfort to many Ulster Protestants. The beleaguered people of Northern Ireland have taken great risks for peace in recent months. Isn't it time the Irish Government seriously considered making a move to rejoin the Commonwealth?

Harry Barnes is a joint president of the British-Irish peace group, New Dialogue, vice-chair of Labour's Northern Ireland Departmental Committee, and a member of the British-Irish Inter-Parliamentary Body.