Massive water pressure caused the polystyrene cups to shrink Enlarge Image

Environment correspondent Mike McKimm travelled 12,850 feet to the wreckage lying in the icy waters of the North Atlantic, getting a fascinating glimpse of the ill-fated liner.

He put a number of polystyrene cups in a net which was trailed outside the Russian submersible on his voyage to the wreckage.

A useful demonstration of the huge water pressure on the submersible and indeed the potential dangers that lurk at the bottom of the ocean, the journalist is auctioning off three cups to raise money for the BBC's annual charity appeal.

One of the cups up for sale on internet auction site eBay has already fetched bids of more than �800, with a second attracting bids of more than �500.

The third cup was sold off on BBC Radio Ulster for �385.

Mike said he got the idea as he stood waiting to climb into the Mir submersible, pondering the effort people had put in for his Titanic trip.

"Suddenly it dawned on me, how to make the most of the unique event that was about to unfold - do something for BBC Children in Need," he said.

Click here for a closer look at the wreck of the Titanic In pictures

"Hurriedly, some polystyrene cups were drawn on and after a bit of begging from fellow travellers, three baseball caps were produced."

He said they were not of any great value at the time, but by the end of the day, he had "the only three baseball caps that had been down to the Titanic, all the way to the bottom of the Atlantic".

"There are special certificates on Harland and Wolff notepaper to prove that. Even that notepaper had been taken all the way down to the wreck," he added.

Mike McKimm said the polystyrene cups were slowly crushed by the massive water pressure as the craft descended towards the sea bed.

"Billions of tons of water producing 6,000 pounds per square inch did its work," he said.

"The cups were squeezed from all sides until they became perfect tiny replicas of themselves - utterly unique and rare as proverbial hen's teeth.

He said they served as an ominous warning of what awaited the journalist and crew if anything went wrong.

"Although it's unlikely I would have come back small but perfectly formed in such a mishap," he added.

You can try to get your hands on one of the three Titanic cups and baseball caps by logging on to the Great Big Bid website, in association with eBay, on: bbc.co.uk/greatbigbid where the remaining two cups and caps will be up for auction all week.