Oscar-winning film director Steve McQueen has thrown his support behind demands for planned anti-slavery laws to be toughened up and for extra protection to stop victims being turned into criminals.

MPs and peers have warned that the government's draft modern slavery bill, which includes measures that will see human traffickers given maximum life terms, does not go far enough and parts "need a rewrite" so the criminal offences are simplified to ensure there are more convictions.

Victims must also be put at the heart of the legislation, with provisions that shield them from prosecution for crimes they were forced to commit while enslaved, the joint committee on the bill said.

McQueen, whose 12 Years A Slave won best picture at the Oscars, said Britain could be "justifiably proud" of its anti-slavery tradition that stretches back to campaigners such as William Wilberforce and the Quakers.

In a statement released by the committee, he added: "The authors of this report can honourably stand in that tradition. They have listened to the evidence and considered it with great care. Their recommendations are humane and principled.

"More than that they have grasped the complexity of contemporary trafficking and forced labour in the United Kingdom and have set forth clearly the fundamentals of what is necessary to tackle it effectively.

"I warmly commend this report and pay tribute to the members of the committee who have produced it. Their work has honoured Parliament and the country."

The committee said estimates about the scale of modern slavery, which includes sex trafficking as well as forced criminal activity and labour, varied widely but it was believed there were thousands of victims of sexual exploitation in the UK.

Victims include British schoolchildren groomed, abducted and forced to have sex and people who are trafficked and enslaved once they are here, it added.

The MPs and peers called for the creation of six offences – slavery of children and adults, child exploitation, exploitation, child trafficking, trafficking, and facilitating the commission of an offence of modern slavery. They pushed for legislation on supply chains to ensure that firms could "no longer turn a blind eye to exploitation occurring in their names" and urged the government to take the lead by "eradicating modern slavery from its own supply chains".

Committee chairman Frank Field said: "The shift to the focus on victims is not only the morally right thing to do in and of itself, it is essential if we are to get the prosecutions necessary to try to end this evil.

"We must conclude that for parts of this bill, amendments will not be sufficient to make good, workable, effective legislation. Some parts of it need a rewrite.

"This is groundbreaking legislation that will influence law and the fight against modern slavery around the globe. The world is watching, we have to get this right. In the 19th century British politicians sought to abolish the international slave trade and end one of the most deplorable practices in history."

Lady Butler-Sloss, who sat on the committee, said: "Unless and until the protection of victims, and the provision of support and services to them, are put on a statutory footing at the heart of this legislation, there is a risk that we will turn victims into criminals. Apart from the fact that this would be morally wrong, it is also self-defeating."

Helen Dickinson, the British Retail Consortium's director general, said: "The BRC absolutely supports the government's efforts to end exploitation of workers in the UK and we understand that retailers have a crucial role to play here.

"All levels of government across the UK also need to take this opportunity to look to themselves and take a lead in eradicating slavery and exploitation by ensuring their own supply chains meet the standards the draft bill sets for the wider private sector."

Karen Bradley, the minister for slavery and organised crime, said: "Modern slavery is an appalling evil, and the home secretary and I are committed to stamping it out. The modern slavery bill, the first of its kind in Europe, represents an historic opportunity to get new legislation on the statute books. It will increase the prosecution and punishment of the organised criminals behind most modern day slavery and strengthen protection for victims.