It had been predicted that this would be the "sticker-shock conversation", and that is how the latest round of nuclear talks turned out. The phrase, for those unfamiliar with American retail jargon, refers to the unpleasant moment a prospective buyer eyes the price label on an object of desire. In Vienna, the object is a lasting compromise on Iran's nuclear programme, and the price came as a shock even to the seasoned diplomats who have been working away at this for years. One senior western diplomat had this to say:

Perhaps expectations had been a little high...On some issues we would have probably expected a little bit more flexibility on their side

A senior US official added:

Everyone is serious here. We know that. But we believe there needs to be some additional realism at this point. As I said, significant gaps remain. We need to see more progress being made. Time is not unlimited here, and we're still tracking towards the July 20th date to see if we can get this done.

And the Iranian deputy foreign minister, Abbas Araqchi, was even blunter:

The talks were serious and constructive but no progress has been made.

The talks have hit a wall, but it is a wall in the sense marathon runners use to describe the moment when they suddenly feel they have no energy and stamina left. Sometimes it stops them dead, but not always. The most determined fight a way through.

It is a commonplace of complex negotiations that the parties come to the talks with their maximalist position and the participants in the Vienna talks have seen no reason to dispense with the tradition. No one was giving away details, but it is a fair bet that the biggest gap was over the capacity of a future Iranian civil nuclear programme, measured in thousands of centrifuges and their output measured in 'separative work units'. The West is thinking in terms of 4,000 to 6,000. An Iranian official at the talks told Reuters his government hoped to have up to 100,000!

The bulk of the progress is often made in the last days or hours of talks when both sides are on the point of walking away from the table. The deadline for these negotiations is July 20, but it is a self-imposed date and will have some give in it.

One way of speeding up the talks might perhaps be to move them to a less comfortable venue. The Palais Coburg hotel is a resplendent and luxurious monument to Vienna's imperial age. It used to belong to the Coburg-Gotha dynasty, relatives of the British royal family. One diplomat claimed, with only mild exaggeration, that his hotel room was bigger than this home.

One of the post-mortem briefings was held in a sort of posh dungeon hollowed out of the sixteenth century city walls below the palace. It is no doubt where the diplomats would like to keep the press, until they have some forward movement to report.