In previous eruptions of violence in Northern Ireland, republican attacks were almost automatically followed by lethal retaliation by loyalist groups whose speciality lay in "tit-for-tat" killings of Catholics.

Now thousands of people across Northern Ireland, and particularly in Co Armagh, are hoping this so-called peacetime means revenge attacks will not be launched, and the violence will not escalate. The illegal loyalist organisations have been unusually quiet in recent months but remain armed and have in the past re-emerged after periods of inactivity.

Very often they go on the warpath with shootings which, they claim, are in retaliation for republican violence.

Security forces are thus on their guard both against the risk of republican and extreme Protestant activity.

Loyalists have a long and bloody record, although during the Troubles both local and international attention was always focused on republicanism and the IRA.

Loyalists have been responsible for 1,100 of the 3,700 deaths, a lethal record which means they have to be taken seriously. Over the past 10 years, indeed, they took more lives.

By far the largest groupings within the paramilitary undergrowth are the Ulster Volunteer Force and the Ulster Defence Association.

One problem in trying to foil their activities at times like this is that most of their victims have been uninvolved Catholic civilians – often chosen at random.

An unusual and potentially heartening sign came yesterday with a meeting between Frankie Gallagher, who offers political advice to the UDA, and Sinn Fein lord mayor of Belfast, Tom Hartley. Mr Hartley said he was encouraged by the encounter while Mr Gallagher said of the meeting: "We've never done this before."

Offering unprecedented praise from a loyalist source for Martin McGuinness's condemnation of dissidents, he added: "The Sinn Fein response has been astonishing.

"They have demonstrated to the people in unionist communities they are now committed and wedded to peace and non-violence."

While his comments are regarded as hugely encouraging, they do not guarantee violence will not emerge from the loyalist undergrowth.

This is because the UDA and UVF contain highly independent localised gangs which act on their own.

In 1994, for example, the UVF shot dead six Catholic men in a quiet Catholic bar in Co Down at a sensitive time in the peace process – not long before the IRA declared a ceasefire.

UVF leaders said privately the attack had not been "centrally authorised", a claim which was widely disbelieved at the time. It later emerged this was almost certainly the case.

That incident illustrates the difficulties of guarding against loyalist violence, since it was staged by gunmen from Belfast who travelled miles to a sleepy Co Down village which had previously been almost unaffected.

A similar pattern was visible around the same time when UDA gunmen kicked open the door of a bar in Greysteel, Co Londonderry, at Hallowe'en. Shouting "Trick or treat" they sprayed the bar with gunfire, killing eight. The third prominent group is the Loyalist Volunteer Force, which broke away from the UVF. The LVF was founded by Billy Wright, a firebrand later assassinated by republicans inside the Maze prison.

Much of the loyalist violence of recent (peacetime) years has been internal feuding, which has left more than a dozen paramilitaries dead.

Few if any of those killings were politically motivated, stemming instead from power struggles, quarrels over territory and personality differences. Most resulted from disputes over the proceeds of crime.

Racketeering, extortion and drugs trade have been rife, particularly in the UDA and LVF, with the latter sometimes described as a drug-dealing organisation with a violent wing.

The UVF and UDA made attempts to emulate republicans in building political wings, but did not succeed in attracting many votes. The UDA disbanded its political wing some years ago while the Progressive Unionist party, which spoke for the UVF, suffered a body blow with the 2007 death from natural causes of David Ervine, its respected leader.

At the less appealing end of the spectrum were a series of grotesque paramilitary leaders such as Jim Gray, a UDA "brigadier" who flouted the proceeds of gangsterism.

His lifestyle was ostentatious, with expensive cars, fine restaurants and a costly cocaine habit. Reputedly bisexual, he sported a shock of bleached hair and permanent tan.

He frequently wore fluorescent clothing and designer sunglasses, and typically dressed in a floral shirt with a pink jumper draped over his shoulders, white trousers, a large earring and a heavy gold necklace. Another UDA leader, now sacked, was known as "the Bacardi brigadier" because of his drinking habits. Yet another was a compulsive gambler who squandered £80,000 of his brigade's funds.

Generations of paramilitarism have produced other eccentric loyalists, and seen groups such as the UDA evolve a blend of criminality and violence – a curious but dangerous mixture.