Without a basis of mutual confidence no new arrangement would have been possible since Unionism has traditionally been mistrustful of successive British governments, regarding them as too ready to do deals with Irish nationalism.
This was obvious in 1995 at the news conference when Mr Trimble declared he was standing for the leadership of his party. Asked what changes he would make he replied: "One small change that I would make, but none the less crucial change - I would never go into Downing Street alone. You've got to have someone else with you to take notes, to observe and to listen carefully, is absolutely crucial, because one must be careful not to be seduced." This amounted to an implicit criticism of Mr Trimble's successor as leader, James Molyneaux, who had based his approach at Westminster on having the ear of prime ministers and others in high places
Mr Molyneaux's departure was precipitated when John Major produced a document which was regarded as distinctly anti-Unionist in tone. This reversal punctured Mr Molyneaux's reputation for having access to the corridors of power.
The high degree of suspicion evident in Mr Trimble's remarks was in marked contrast to the scene at Hillsborough Castle earlier this week when the cameras caught a shirt-sleeved Tony Blair leading the Unionist leader to his car.
While their body language could not be described as relaxed, it did seem to speak of a business-like relationship; and the fact that no other Unionist was there "to take notes, to observe and to listen carefully" spoke volumes. Mr Trimble has seemed to repose more and more trust in the Prime Minister. One feature of the Unionist party's relations with the government is that many of its senior members are unremittingly hostile to the Secretary of State for Northern Ireland, Mo Mowlam, with some of them openly rude to her face. They claim she is "too green", finding Mr Blair much more to their taste.
Mr Blair privately spelt out the basis of his approach to Unionism when he spoke to Irish-American figures in Washington in February. His private secretary's note of the meeting was later leaked.
According to this account: "The Prime Minister said that the Unionist community felt isolated in many ways. The Irish government supported the nationalist side, whereas the British government obviously had to take account of both communities. This led the Unionists to tend to resist all change.
"The important thing was that the Unionists had signed up to North-South structures. As far as Trimble was concerned he had come a good deal further than many Unionists wanted him to, for example accepting North-South structures. It was important to remember that Trimble was under constant attack from Paisley and McCartney, so that giving comfort to the Ulster Unionists was vital."
Mr Blair said national boundaries were becoming less relevant over time, describing the Republic of Ireland as a go-ahead, open and modern society. But he returned to Mr Trimble's difficulties, saying he "had to be an advocate of change without making himself vulnerable to charges of betrayal".
It seems clear from this that he has carefully assessed the Unionist leader as a potential moderniser, around whom the basis of a new deal could be built. This means he will do all he can to safeguard and support Mr Trimble in his coming battles with the Rev Ian Paisley and other opponents of a deal.