They seized computers, mobile telephones and documentation thought to include false papers and passports.

No arrests were made, but Detective Superintendent Mick Gradwell, who is leading the investigation, said that his detectives hoped to do so “within days rather than weeks”. He added: “I can only repeat that the investigation team are determined to find those people responsible for this tragedy.”

Police are now “interrogating” the computers’ hard drives in an attempt to identify the staging posts on the journey that took the labourers from mainland China to poverty, exploitation and death in Britain. Steven Finnigan, the Deputy Chief Constable of Lancashire, said: “The scale of this inquiry is truly massive and could take us to all parts of the globe.”

Mr Gradwell said: “They have probably paid a lot of money to come here. Once here they have been living in appalling conditions and certainly working that way.

“We have traced some to four or five-bedroom houses where up to 40 people have been residing. They are cramped with mattresses slung on the floor and hardly evidence of food to feed them.

“When they went on to the bay they were not properly equipped and they went out there at the wrong time. It all adds up to a very tragic picture.”

Detectives acknowledged that, even with the help of translators skilled in Cantonese and Mandarin, formal identification of the dead and 16 survivors — the majority illegal immigrants — remains incomplete. Mr Finnigan described the debriefing process as “painstaking”. The survivors, who were paid as little as £1 for a day’s labour, remained fearful of gangmasters who ruled their lives. He said: “There is a feeling that some of the survivors remain reticent and apprehensive. We need to get to the bottom of that and find out why they are not as open as we would like.”

The fear is only too evident among the Chinese labourers still housed in dilapidated terraced houses in the Morecambe and Heysham districts.

Wang Wen, 22, is the only woman among 13 cocklers and the only English speaker in a sparsely furnished and unheated flat. “I pray not to hear the sound of boss’s minibus outside,” she said. “We are shocked by what has happened. We are scared to go out fishing but we must go back because it is our only work. We do not pay any rent because we fish. Our boss gives us this house free. If we do not fish we have nowhere to live.”

Ms Wang, who sleeps on a blow-up mattress, has a work permit. “I left China for many reasons,” she said. “It is a better life in England. I have a work permit and want to stay three or four years. This is a good group. We never go out fishing when it is night or when the tide is in.

“We do not read English and have no television so we do not really know what is going on. We are just told we must fish this week. The boss says he needs the money. I am really scared.”

Among the houses raided by police were two along Deane Road, in the Kensington area of Liverpool. Neighbours said they had seen Chinese men and women unloading bags of cockles from Transit vans in the early hours over the past year. They pinpointed one better-dressed Chinese man as the group leader. “He is more intimidating than the rest of the group and they always seem to follow him round,” one neighbour said.

Outside the house, the Chinese man angrily confronted reporters and photographers before snatching a camera and hurling it into a rubbish bin.

In Morecambe, residents left bouquets of flowers anchored by pebbles on the windswept beaches yesterday. Chief Superintendent Wendy Walker, division commander, said that there were already plans for a permanent memorial. “Even though the victims were not from here, local people are grieving,” she said. Prayers were said for the victims at a special service at the Chinese Christian church in Manchester.

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