The Aslef rail union announced on Thursday that 450 of its members in central England would walk out between August 6 and 8 in a dispute over pensions, affecting passengers travelling from cities such as Sheffield, Nottingham and Derby to the capital.

The decision coincided with a move by border officials to strike on July 26, the day before the start of the Games, potentially delaying thousands of visitors arriving for the showpiece event.

The threat of transport chaos added to pressure on the government, which has already had to call in thousands of extra soldiers to guard the Games after a failed private sector recruitment drive left an embarrassing hole in security.

Even the wet weather has conspired to dampen spirits ahead of the sporting showcase, which has earned the nickname the "Soggy Olympics" in the British media.

Perhaps it was no coincidence that Police lyrics "sending out an SOS", from the song "Message in a Bottle", were blaring before the daily press conference at the Olympic Park in east London.

Culture Secretary Jeremy Hunt rejected accusations that the buildup to the Games had been a shambles, arguing that for an operation of such a scale the preparations had in fact been remarkably smooth.

"Actually I think it has been a very smooth process," he told reporters, after a barrage of questions on issues ranging from security shortfalls to sanitation on the main Olympic site. "I think it has been an encouraging first week.

"I think it is very important that people understand that of course you are going to have a few hitches on a project of this scale, but actually things have gone pretty smoothly, and the athletes are getting a fantastic welcome in the village, and I think morale is very high."

On the issue of the danger of strike action causing disruptions, he added: "It would be completely out of tune with the mood of the British public. This is a moment when Britain wants to show its best face to the world, and that is what the vast majority of the public wants as well.

"I would strongly counsel any unions thinking of disrupting this very important period, I think they would lose huge amounts of public support if they really tried to do this."

Prime Minister David Cameron, speaking during a visit to Afghanistan, said of the planned action by passport officials: "I do not believe it would be justified."

GUARD SHORTFALL

The security glitch came after G4S (GFS.L) said it could not provide a promised 10,400 security guards to staff Games venues, meaning the Defence Ministry had to call up an extra 3,500 troops to take the armed forces contribution to 17,000 personnel.

A further 2,000 troops may be required if security firm G4S fails to find a minimum requirement of 7,000 staff.

Hunt reiterated government assurances that the Games would be safe in a city where suicide bombers killed 52 people in attacks on the transport system in July 2005.

Further concerns could be raised by Wednesday's suicide bomb attack on a bus transporting Israeli tourists at Burgas airport in Bulgaria.

"Obviously we are monitoring the whole time what's happening with respect to the changing security situation, and we have extremely competent intelligence services who are giving us advice and we are responding to that on an ongoing basis," Hunt said when asked about the Burgas attack.

"The world can be absolutely certain that we will deliver a safe and secure Olympics. It has always been our number one priority."

OPENING CEREMONY

With the Games eight days away, British media has focused heavily on the opening ceremony amid reports of tensions between Oscar-winning film director Danny Boyle, who is overseeing the 27 million pound show, and the Olympic Broadcasting Services in charge of airing the Games.

According to the Guardian newspaper, quoting an unnamed source, the atmosphere between the two was "miserable" and rehearsals were behind.

The July 27 evening ceremony, to be watched by a global audience estimated at more than a billion people, has already been shortened to avoid a possible late-night rush for trains and buses home.

"I think I would expect there to be lots of negotiations going on behind the scenes, but I think the overall picture is very encouraging," Hunt said, explaining that he was not aware of the specific problems being reported.

"I think it is going to be a sensational opening ceremony. It will show the best of Britain - its history, its culture, our contribution to the world. But it will do it through the artistic vision of one our finest film directors."

The ceremony will feature more than 10,000 performers and include the recreation of an idyllic English rural scene complete with live animals. (Additional reporting by Mohammed Abbas in Kabul and Peter Griffiths and Michael Holden in London; Writing by Mike Collett-White; Editing by Alison Williams)

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