ASIDE from Blackburn, and possibly Iraq, the single issue which has taken up more of my time during the nearly five years I have been Foreign Secretary is Iran.

When I first took over in Spring 2001 from Robin Cook the big question was whether I should visit the country. No Foreign Secretary had been there since the revolution of 1979.

Relations had been severely strained and the "fatwa" an official decision to target for assassination the author and British citizen Salman Rushdie in 1989 made matters much worse.

In 1997, relations began to thaw. Unexpectedly, the presidential election was won by a reformer, Mohammed Khatami. The fatwa was lifted; our diplomatic relations upgraded. After some false starts I became the first British Foreign Secretary to visit Tehran in a generation, in September 2001.

It was quite a trip, My visit to Iran followed one to Israel. The Israelis did not want us to improve relations, and they also took exception to a milk-and-water article I had written which dared to use the word "Palestine."

Everybody uses the term now and quite right. But then so far as many Israelis were concerned, even admitting the possibility of a separate State of Palestine was a step too far.

But for all the problems and issues surrounding it I think the trip did make a difference. I have been back to Tehran four times since and I would like to visit some of the rest of this populous (70 million plus) country with its distinguished history and civilisation.

But that will have to wait, I fear, for calmer times. Meanwhile I am in the middle of the current episode of "Iran nuclear."

The story so far is this. Iran is a signatory to the "Non-Proliferation Treaty" (NPT). Back in the early 1960s there were predictions that by 2000 there could be 30 or more states with nuclear weapons, with the highest prospect of a nuclear war.

So the NPT was agreed a deal struck between the "Permanent Five" (P5) of the UN Secretary Council and the rest of the world. The P5 (US, UK, Russia, China and France) would keep their nuclear weapons but gradually reduce their arsenals. All other countries would give up any nuclear weapon ambitions, but would be guaranteed the right to the peaceful use of nuclear energy, for example to generate electricity by nuclear power.

The deal has worked pretty well. In addition to the P5, there are only three countries with nuclear weapons capability for sure India, Pakistan and Israel and these three are not signatories to the NPT. Iraq and Libya had programmes, but no longer. North Korea remains a problem.

As for Iran it began a civil nuclear power programme in the 1970s under the old pre-Revolutionary monarchy; that's still going.

In 2002 it emerged that Iran, contrary to its obligations, under the NPT, had been hiding its work on the most sensitive of all nuclear technologies uranium enrichment.

Low enriched uranium (LEU) is needed as fuel for power stations, but once you have that its not difficult to turn it into highly enriched uranium (HEU) for use in a nuclear bomb.

We do not have concrete evidence that this is what Iran wants to do: but there is sufficient circumstantial evidence to warrant concern. With France and Germany I have been trying to negotiate on all this with the Iranians for nearly three years.

It is essential that we bring the matter to the satisfactory conclusion that Iran provides the international community with "objective guarantees" about its programmes.