There is "definite cause for optimism" after a day of talks with the hijackers of an Afghan airliner at the UK's Stansted airport, police have said.

The Ariana Boeing 727 has been on the ground at the Essex airport since Monday morning, when it arrived after being hijacked on an internal flight in Afghanistan and flown across Russia and Kazakhstan.

As the 151 passengers spend their third night on British soil, the hijack has become the longest in UK history.

But Assistant Chief Constable Joe Edwards, of Essex police, said there was definite cause for optimism after a day of "constructive" talks.

He said he felt "much more hopeful" of a peaceful conclusion than he had on Tuesday night, when four members of the crew enraged the hijackers by escaping the plane.

Asylum speculation

Four of the hijackers, armed with handguns, left the plane on Wednesday night to help load food parcels for the passengers.

Police have said they are fairly confident that the hijackers are also carrying grenades and knives.

There has been speculation in London that the hijackers - believed to number between six and 10 - are simply seeking political asylum.

But Mr Edwards said it was more complex and added: "The detail of the negotiations are about what is the key to getting everybody off that plane willingly and unharmed and that is a complex situation.

"If it was as easy as some of the press speculation suggests - that they simply arrived here to achieve certain pre-set aims - why are they there three days later?"

Earlier, the head of Ariana Mullah Hamidullah said a steward who had been released during a stopover in Tashkent, Uzbekistan, said there appeared to be a large group on the aircraft of up to 40 men, women and children who could be involved in an attempt to get political asylum.

Click here to watch live coverage of the hijack.

An official from the United Nations High Commission for Refugees has arrived at the airport, although spokesman Paul Wilkinson refused to comment on whether political asylum was the reason for the hijack.

He said the organisation was able to provide information about the situation in Afghanistan but said any requests for asylum would be dealt with by the British authorities.

But he added: "Conditions in Afghanistan are very very bad, very very miserable and people are often driven to extremes in these circumstances - especially when it has been going on so long and no end is in sight."

Eman Omar, a solicitor who represented a gang responsible for Britain's last hijack crisis, in 1996, said she believed the Stansted group were "highly likely" to be seeking asylum in the UK.

If the hijackers do try to claim political asylum in the UK, they may be encouraged by the fates of others involved in similar incidents.

International law

Six members of a gang that forced a hijacked Sudanese jet to Britain in 1996 are still living in the UK on benefits while they await an adjudication on their claims, while a man involved in a 1982 Air Tanzania hijack was granted asylum here after serving two years of a three-year jail sentence.

Under international law the UK is obliged to consider any asylum claim submitted once any potential criminal proceedings are completed.

Police have already established that the hijackers are carrying handguns.

The familiar routine of recent days has now been re-established, with hot food and medical supplies being delivered to the plane, in a quiet corner of Stansted Airport.

Four hours later a flight attendant was pushed down the steps. He was treated for a minor cut on his forehead.

Police said they were unable to speak to the hijackers at all for about an hour afterwards.

In Afghanistan, the ruling Taleban movement has arrested 10 people in charge of security at Kabul airport over the hijacking.

Also:

Pilots criticised for fleeing
Hostages 'face horrific ordeal'
Who are the hijackers?
Negotiating with hijackers
Stansted's hijack history