It was the loud thud that woke Norwich GP Cath Robinson, a passenger on the final voyage of the MS Explorer. “It was about midnight, and we’d been going through pack ice, so I was used to scrunching and scraping noises, but this was different,” she says. “We had hit an iceberg.

“An alarm went off and, as the crew were called to muster stations, the announcer said, ‘This is a real emergency.’ We were told to dress in very warm clothes and life jackets, and go to emergency points. “We had done an emergency drill, but I never thought we’d do it for real.”

After four hours adrift in open boats, all 154 souls were saved, but the MS Explorer – a 38-year-old polar veteran – was lost in 4,000ft of icy water. The sinking has sent shudders through the Antarctic cruising industry, with some commentators warning that these seas will one day be the scene of “the worst maritime disaster in world history”.

Dr John Shears, a specialist in polar policy from the British Antarctic Survey, whose own research vessel, the RRS James Clark Ross, was damaged after striking rocks in November, says that the relatively small operation to rescue Explorer’s survivors “took the combined resources of several cruise ships”. It proves, he adds, that “providing effective assistance in the event of a larger ship going down would be incredibly difficult”.

Make that impossible, says Martin Gray, a veteran mariner and Antarctic guide. “In the past year or so, we’ve lost the Explorer, had the MS Fram lose power and drift into an iceberg, the MS Nordkapp suffer an 80ft gash in her side after hitting rocks, and even a ship as experienced as the James Clark Ross get into trouble. This proves that, despite being specifically built for these conditions, these ships are still hugely vulnerable. Imagine the potential for disaster in a ship that isn’t ice-strengthened, with 10 or 20 times as many passengers on board.

“There are no kindly coastguards in Antarctica looking out for you, and there is no search-and-rescue infrastructure. My heart sinks when I see these liners with 3,000-odd souls heading south,” he says. “Because, when something goes wrong, there will be massive loss of life.”

Antarctica has become the must-see destination for the cruising crowd. Last year, 58 ships took 37,550 passengers into Antarctic waters, an increase of 25% on 2006.

The majority of visitors sailed on small, ice-strengthened expedition vessels, but with demand to see ice and penguins spiralling - “before it’s too late”, as one passenger puts it - cruise lines such as Princess Cruises and Holland America face huge temptations to divert vast floating hotels from familiar cruising grounds such as the Caribbean to the poorly charted waters of the Antarctic Peninsula.

The Passenger Shipping Association insists that the cruise industry is “committed to providing a secure environment for its passengers and crew”, yet maritime safety experts say that many of the large cruise ships visiting the Antarctic Peninsula are dangerously unsuitable for the job.

These range from the Delphin Voyager, which carries 650 passengers, through the Rotterdam, carrying 1,668, to the vast Star Princess and the Golden Princess, each accommodating 3,100. All these ships, says Allan Graveson of the seafarers’ union Nautilus, are accidents waiting to happen.

“There are two aspects to the risk,” he says. “The first is their construction. Ships operating in polar waters should be built to an ice-class specification from D-class steel, but ships like the Princess class aren’t even built for the North Atlantic.” The shipping insurer Lloyd’s Register confirmed that just two of the 10 biggest ships operating in Antarctica – the Marco Polo and the Deutschland – have ice-class ratings.

The second issue, according to Graveson, is lifeboat capacity. “These ships all meet international safety requirements - as did the Titanic - but they don’t provide for survival because cruise-line mentality says that no matter how damaged a ship is, it will always make it back to port.

"When one of these hits an iceberg, the lucky ones will get aboard davit-launched lifeboats. The unlucky ones will face a 50ft jump into icy water and a swim to a rubber raft. You have to ask how many would survive the jump, let alone the hypothermia.”

Princess Cruises’ huge Star Princess embarked on her latest Antarctic cruise last Thursday, and the cruise line insists that passengers who’ve paid up to £5,879 for the 12-day voyage have nothing to fear. “Star Princess will sail in the relatively ice-free waters of the western side of the Antarctic Peninsula during the height of the summer season,” it explains.

“The ship will be carrying a captain and other mariners with experience of cruising through Antarctica.” And experience, says Captain Bob Tarrant, of the Royal Navy ice-survey ship HMS Endurance – currently searching for the wreck of the Explorer – is essential.

“The Antarctic Peninsula is largely unsurveyed,” he says. “With none of the navigational aids one encounters elsewhere in the world, mariners are reliant on constant vigilance, skills and prior experience. Maritime operations in this part of the world are expeditions, not vacations.”

Denise Landau, executive director of the International Association of Antarctic Tour Operators (IAATO), says many cruise-ship passengers are oblivious to the risks. “Cruising in Antarctica is inherently dangerous,” she says. “But the IAATO cannot tell cruise lines to limit the size of their ships. That’s a job for governments.”

And don’t think heading north is going to be any safer: Professor Rob Huebert, of the University of Calgary, warns that the centuries-old charts still used to navigate Arctic waters pose a serious risk to cruise-ship safety.

“As the ice recedes, we are realising that our charting is abysmal,” he says, “and if you go into waters that you think are relatively deep and relatively safe, because the chart tells you that, but it turns out the chart is wrong, that is where you have these huge accidents.”

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