CAMPAIGNERS are urging a Scottish firm to investigate allegations of "modern slavery" against a company with which it is involved in a major joint venture in India.

The Blood Bricks campaign, which aims to highlight cases of bonded and child labour, says it has uncovered a case involving seven labourers who said they were made to work for two months without being paid any wages and faced serious exploitation, including having to work up to 18 hours a day and physical abuse.

The workers were said to have been working for Jai and Raj Group, a sub-contractor of Indian engineering and construction giant Larsen and Toubro (L&T) Ltd.

In 2010, Renfrew firm Howden Group entered into a multimillion-pound joint venture with L&T to manufacture equipment for power plants.

Now campaigners have written to Howden Group alerting the firm to the allegations, which have been passed to the Indian Government's Ministry of Labour.

The workers from the state of Uttar Pradesh were said to have been lured to work by an advance of 1000 rupees (£10.26) and promised wages of 12,000 rupees (£123.08) a month to work on a construction site in Delhi.

Andrew Brady, project director at Union Solidarity ­International (USi), said the allegations potentially ­implicating L&T were a "serious breach of domestic and international law". He said: "If companies want to ­operate in the UK, then this must come at a price of proactively ­ensuring their supply chains are free from slavery or, if they are UK companies operating around the world, then they have a legal duty to uphold the law.

"If they do not then we will use whatever means necessary to hold them to account."

The Blood Bricks campaign, which involves trade unions, NGOs and local people, is working to tackle the issue of an estimated 10 million people in India who are bonded labourers or "modern slaves".

Most of the issue centres around the country's brick industry, with workers usually lured by a broker from poor, rural communities with promises of work.

The workers are then charged a fee by the broker that can take a li­fetime to repay as payments are so low.

In one shocking case uncovered by the campaign, a man who escaped from his job was captured again - and told he had to choose between his life, his leg or his hand.

His hand was subsequently chopped off with an axe.

Jim Sheridan, Labour MP for ­Paisley and Renfrewshire North, who is backing the campaign, said the issue strengthened the case for the Modern Slavery Bill, which is going through Parliament and includes a requirement for large companies to disclose what action they have taken to ensure their supply chains are "slavery free".

Sheridan said: "It is building up the case to make sure that British companies don't get involved in such things and make sure employees are treated abroad the same way they would be treated in this country."

Patrick McGuire of Thompsons Solicitors in Scotland, which is a partner in the campaign, called for punishments such as fines and compensation claims from victims for any UK firm found to be involved in human rights breaches in their supply chain, either directly or through involvement with another company.

In a statement, Howden confirmed it was in a joint venture with Larsen and Toubro in the power industry in India.

But it added: "However, we are not aware of any issues around bonded or forced labour (or allegations thereof) in connection with L&T or a subcontractor of L&T in India.

"Howden has a strong focus on corporate citizenship and adheres to strict rules and standards regarding its employment practices, and refrains from and denounces any form of bonded labour."

A spokesman for L&T denied the allegations of bonded labour and said the company had the highest standards of labour welfare at all establishments and job sites, and was compliant with the Indian labour laws and acts.

He added: "Among other rules and regulations, there are specific checks in place that prohibit the use of bonded labour.

"We understand from our project site that we hire various equipment from the agency (Jai and Raj), and confirm that no bonded labour is deployed at our project site, directly or indirectly.

"A few days back, the agency's workmen had raised some wage dispute with them, and that was amicably resolved by the agency."