If proof were needed that a picture is worth a thousand words, the silent images of three suspected IRA men standing between two Colombian military police provide it.

They have superseded the several thousand words in the Irish and British governments' implementation proposals, the de Chastelain report and the IRA statements on decommissioning and not decommissioning. The stunned official silence in Dublin and London is evidence of that.

Quite simply, the TV pictures from Bogota make the prospect of working the institutions of the agreement bleaker now than at any time since the agreement was signed. As things stand, it is impossible for Mr David Trimble to go forward for election as First Minister on or before the legal deadline of September 24th.

Before the revelations from Colombia, Mr Trimble was one vote short in his own party of the number needed to secure majority unionist support. Now even his pro-agreement Assembly members would not permit him to stand.

The implementation proposals the governments presented after the Weston Park talks were a shock for unionists in Mr Trimble's party. The DUP was furious. The detailed changes in policing and demilitarisation, amnesty for fugitives and the arrangements to prevent Mr Trimble curtailing the ministerial functions of Sinn Fein ministers were all predicated on an unprecedented statement about IRA weapons from Gen John de Chastelain's decommissioning body.

When it came, Mr Trimble rejected it as insufficient. Essentially, he is sticking to his line "no guns, no government".

Republicans were outraged. They say all the changes should have been implemented ages ago, that the British have dithered and obstructed and sided with Mr Trimble, whom the courts have found in breach of the agreement. The republican line is "no government, no guns".

A complete impasse then, to be negotiated away in six weeks. Not now. It's the pro-agreement unionists who want answers about Colombia. As Sir Reg Empey, the North's Industry Minister, said, the three suspected IRA men didn't go there for a tan.

Mr Michael McGimpsey, the Culture Minister and most moderate unionist in the executive, has demanded a full explanation from Mr Gerry Adams; no "evasions or lame excuses".

Republicans don't seem to realise how much damage the Colombian escapade has done to pro-agreement unionists. Mr McGimpsey has said: "No one should underestimate the damage to unionist goodwill towards sharing power with Sinn Fein".

The anti-brigade are chanting "Told you so". Men like Mr McGimpsey and Sir Reg are fearful they have been taken for suckers. The release of the intricately-detailed implementation plan on policing and publication of changes in criminal justice procedures will tighten the screw on pro-agreement unionists two more turns.

On previous occasions the anti-agreement faction in the Ulster Unionist Party would have called a meeting of the Ulster Unionist Council to tie Mr Trimble's hands. This time it did not need to. The proposals released so far have united unionists more firmly than for years. Ominously, some members of Mr Trimble's party have said they would not vote to reinstate the institutions even if the IRA handed over weapons.

Colombia makes any concessions by unionists impossible. Those slightly blurred images will flicker repeatedly on TV over the next few weeks. The slow trickle of information, the uncertainty, will keep the story alive and fuel unionist paranoia. Will the men be charged? When will they be charged? What charges? How damaging will the evidence be? Are they linked to the Army Council who are in communication with Gen de Chastelain?

There is another difficulty. All the parties know that now there is a real prospect of an election if talks fail. No party will want to give any hostages to fortune in talks in case they have to fight an election exposed to that most damning accusation in the North: having "sold the pass".

In these circumstances, therefore, it is unlikely that attempts by the British administration to cajole the SDLP into endorsing the new police service will succeed. Not if Sinn Fein is holding out for more. Likewise, it is preposterous to suggest the Ulster Unionist Party will acquiesce in the reforms to police and justice, thereby opening its flank to the DUP.

What if there is not an election and the British government suspends the institutions? This is the most dangerous scenario. An indefinite suspension like Mr Peter Mandelson's action in 2000 risks destabilising the republican movement. The agreement is holy writ for republicans, which they believe the British have no right to tamper with unilaterally.

Republicans view the Suspension Act as illegal and unacceptable because it is British interference in Irish self-determination. As it is, republicans are very unhappy about what they see as the cavalier attitude of the British administration in the North towards the working of the agreement. There is no First Minister, the all-Ireland bodies don't function and the British didn't deliver on the deal they agreed in May 2000.

More serious in the short term is seething anger over the nightly attacks with pipe-bombs, petrol-bombs and occasional gunfire which the UDA and LVF have been orchestrating east of the Bann and especially in north Belfast. There have been two murders.

Sinn Fein believes this campaign is designed to provoke the IRA into breaking its ceasefire. In the event of an indefinite suspension, in other words a political vacuum, there would be no Sinn Fein ministers to expel from an executive if the IRA retaliated as the defenders of Catholics.

Infinitely preferable to either an election or suspension would be a successful outcome to negotiations in September. A few days ago it was assumed a starting point for talks should be an attempt to have the IRA restore its agreement with Gen de Chastelain. That was then.

After those TV pictures the atmosphere is so bad that unionists will be demanding an explanation of the Colombia connection even before they agree to talks, never mind contemplating sharing an executive with Sinn Fein. The space for politics in the North is reducing.

Brian Feeney is a journalist and political commentator in Belfast