The long, dishonourable tradition of spying in Ireland

British forces and Irish republicans have been spying on each other for as long as anyone can remember, to such an extent that the latest espionage developments are in one sense just the most recent in a continuum.

Perhaps the greatest surprise lies in the fact that republicans appear to have continued to devote so many resources to political surveillance in what is supposed to be a new post-Troubles era.

The picture now emerging is that a special IRA unit, headed by a well-known west Belfast republican veteran once acquitted of murder, has been carrying out systematic surveillance on what the IRA used to call "the British war machine". The unit has been keeping tabs on the Northern Ireland Office, the Army, police officers, the Prison Service and in all probability other sections of the administration.

It has also targeted political opponents such as David Trimble of the Ulster Unionists and Mark Durkan of the nationalist Social Democratic and Labour Party. No one is really sure what else it may have been up to, though police are investigating.

The material amassed by its agents has been huge. It encompasses political material, such as details of conversations between Tony Blair and other leaders, and sensitive security material such as the addresses of prison warders.

All of this has the sanction of republican tradition. Michael Collins, a founder of the IRA, had spies and agents in Dublin and Belfast and sometimes used the information he was given for assassinations.

In the 1970s and 1980s the IRA "turned" at least one police officer and a number of prison officers. Only last month the existence of a high-level republican agent was revealed by Brendan Anderson in his book Joe Cahill – a life in the IRA. In the early 1970s, that individual worked in the office of Brian Faulkner, one of David Trimble's predecessors as leader of the Ulster Unionist party, passing out information to the IRA's Belfast Brigade. The sense of déja vu is strong.

Unionists themselves have a tradition of receiving leaks from within government. The Rev Ian Paisley has produced a string of documents from the administration and the police, while members of Mr Trimble's party have on numerous occasions brandished classified documents.

There was a rash of these during Mo Mowlam's spell as Northern Ireland Secretary, giving the strong impression that the administration included quite a few who disapproved of her support for the peace process.

Part of the republican justification for the persistence of such activities on their part lies in the certain knowledge that British intelligence agencies continue to watch the IRA and Sinn Fein. A few years ago it was revealed that one such agency had installed a sophisticated bugging device in a car used by the Sinn Fein leaders Gerry Adams and Martin McGuinness. Both affected to be scandalised when they found out.

Senior police sources say that several years ago a British minister inadvertently revealed the location of another valuable bugging device during a meeting with a Sinn Fein figure. When the Sinn Fein man denied charges that the IRA was responsible for a particular attack, the minister is said to have exclaimed, "Don't give me that – you were heard giving the order."

Republicans searched a house in Belfast, and shortly afterwards put on display an electronic device said to have been hidden in the rafters. It had been ingeniously built into an old piece of wood.

On another occasion republicans produced what appeared to be a leaf-strewn piece of rotting wood, which on closer examination proved to be a well-camouflaged camera. It has been planted near the home of a republican figure.

In addition to technological means, intelligence agencies have, over the years, recruited hundreds of informers within the ranks of republican and loyalist organisations.

This is itself part of a well-established, if not exactly honourable, tradition of infiltrating underground groups. The rebellion of 1798, in which both Catholics and Presbyterians rose against the Crown, failed in large part because a network of informers kept the authorities informed of the plans of the rebels.

But even though informers, agents and bugs have long been familiar features of the Irish conflict, the decision of republicans to keep indulging in the spying game is costing them dearly in political terms.

A few weeks ago it looked as though the Unionists were about to cause the collapse of the Stormont Assembly and power-sharing Executive, but the revelations of republican espionage meant that the IRA and Sinn Fein took most of the blame.

The latest development will cause further damage to the republican image, while simultaneously strengthening the arguments of hardline Unionists who do not want to go back into government with Sinn Fein.