Jack Straw, the Foreign Secretary, will tomorrow make clear to Teheran that the time for prevaricating over its pursuit of a nuclear capability is over.
Mr Straw has made Teheran his first stop at the start of a Middle East tour to drive home the significance of western demands that Iran cease its nuclear weapons development programme and cut links to terrorists.
Visiting Teheran for the fourth time since diplomatic relations were resumed in April 1999, Mr Straw will be exploiting Britain's unique position as an "honest broker" in setting out Europe's preference for persuasion as an alternative to America's belief in "force" as alternative methods of ensuring Iranian compliance. He will make it clear that if Europe's way does not convince, there is only one other choice.
Condeleezza Rice, the US national security adviser, said in London on Thursday that Washington would prefer not to have to use a "Made in America solution" to Iran's nuclear pursuits.
Although British officials steer away from any talk of "deadlines", it will be made clear to Teheran that it needs to allow wider access to UN inspectors within the next two months.
If that is not achieved, Mr Straw will explain, then the resumption in September of EU discussions over granting trade concessions to Iran are unlikely to provide Teheran with much of substance to look forward to.
More specifically, Mr Straw will tell Kamal Kharazzi, his counterpart, at a meeting tomorrow evening that the EU expects Iran to sign up to the International Atomic Energy Agency's additional protocol on weapons inspections over which it has been dragging its feet for several months.
Mr Straw will make clear that there is a "sense of urgency" within the international community for Teheran to prove that it is not developing nuclear weapons.
British officials admitted their task of convincing Iran to comply with international demands "is not going to be straightforward and we are still waiting for the Iranian regime to address our concerns".
They conceded that Mr Straw would be "very much feeling his way" in talks, but that Iran was a vital element to get right if a new political era were to be created in the Middle East.
"Iran is a very important country where, if the reform process succeeds, it will have enormous impact on the entire region. While we can expect both sides to stick to the script in public, what is important is what happens behind the scenes."
Mr Straw will be also be discussing Teheran's alleged links with terrorists amid reports that senior members of al-Qa'eda have been operating out of remote border regions in Iran and in some cases slipping in and out of Afghanistan and Pakistan at will.
The Iranian regime denies the claims, but has privately admitted that it might not be aware of every instance of illegal activity along its 500 miles of common border.
British officials admit to concerns over Iraqi attempts to gain political influence in neighbouring Iran, particularly through the Shi'ite Badr Brigade, the military wing of an Iraqi opposition group with links to Teheran.
