A group of migrant labourers have been freed by police after being forced to work as slaves in horrific conditions for the son of a local Communist Party chief.

They had survived on steamed bread and water for more than a year and eight of the thirty-one were so traumatised that they were unable even to remember their own names, state media said.

Residents of Caosheng village in the northwestern Shanxi province said that the only reason the illegal brickworks had been allowed to operate for so long was because Wang Dongji, the party secretary, was the father of the factory boss, Wang Binbin, One worker, identified as Zhao Yanbin, was beaten to death with a hammer last December and his body wrapped in plastic and buried on a near-by hillside, the survivors told police. Those found in the police swoop had bruises, wounds and burns all over their bodies from having been forced to carry still-hot bricks and to walk barefoot in the kiln.

The men had been unable to wash, change their clothes or clean their teeth in the 18 months since they were duped with the prospect of a job and left the trains on which they were travelling in search of work in the cities, the Shanxi Evening News said. “The grime on their bodies was so thick it could be scraped off with a knife,” it said.

Inside the brickworks, they were watched by five guards with six dogs, to make sure that no one could escape. They were forced to work every day from 5am until after midnight and received no pay.

The foreman’s son and one of the guards had been detained by police, but the foreman and four others were on the run. The brickworks boss, Wang Binbin, who has also been detained, told police that the foreman gave him 360 yuan (£23) for every 10,000 bricks produced. He said that it cost him 0.036 yuan to produce a brick and he could make a profit ten times that on his sales on the market.

Accommodation had been found for the workers in the village while the Government tried to get their wages. Officials were also trying to trace the homes of the eight men so that they could return, the newspaper said.

Millions of migrant workers from poor rural areas flock to urban areas of China each year in search of work, hoping for a share of the fruits of an economy clocking near double-digit growth.

Working for £1 a day or less, they have helped to turn China into the workshop of the world and one of the biggest economies. Many work without formal contracts and have little recourse to the law when disputes occur.

The discovery was made public just as the Communist Party, which has ruled China with an iron grip since 1949, stepped up its campaign against corruption, announcing leniency for dishonest officials who confess but pledging not to allow a single wrongdoer to escape the crackdown.

The latest directive from the party’s watchdog of probity, the Central Discipline Inspection Commission, said that officials had until the end of the month to admit their guilt – although those already under suspicion who try to return their ill-gotten gains would not be spared.

The directive said: “Leniency can be considered if they take the initiative to tell of their problems. Those who refuse . . . will be seriously dealt with.”

It did not say how the party would have more success than in the past in its attempts to curb corruption.

Shady civil servants are coming up with ever more cunning schemes to avoid detection.

Some officials have understandings with businessmen to provide a favour in advance and receive the reward after leaving their jobs – a practice that the Chinese media calls “bribe futures”.

Under the new regulations, officials are banned from running companies with money-men who also give them handsome dividends. They are also prevented from taking earnings from stocks or futures that they did not actually buy.

Other blacklisted bribery includes well-paid nominal jobs – usually for relatives of the officials – as well as buying property or cars at prices conspicuously lower than those on the open market.