There is more slavery now than there was at the height of the slave trade, former Conservative leader William Hague has warned.
Mr Hague said criminal gangs were blighting the UK with the problem, with women pressed into prostitution.
Asylum plans unveiled by the Tories on leader Michael Howard would help address the problem, said Mr Hague.
As the pre-election campaign continues, the Tory MP predicted the poll would be "very close indeed".
Tony Blair now enjoyed none of the popularity which saw him defeat the Tories by a landslide in 2001, he said.
Mr Hague warned about the dangers of slavery in a lecture for the Centre for Social Justice on Monday.
He told BBC Radio 4's Today programme: "The distressing truth is that there appear to be more slaves in the world today than there were transported across the Atlantic in the entire period of the trans-Atlantic slave trade."
People were tricked into loans or paid to be smuggled by people smugglers into developed countries.
Often they never succeeded in paying off their loans and were told that if they stopped working on the black market their families would be made homeless or killed.
Mr Hague said Home Office figures showed 1,400 women were trafficked into the UK each year - part of a $13bn international industry.
Penalties had been toughened up by the government's changes to immigration and sex offences laws, he said.
But he urged ministers to use their presidencies of the European Union and G8 this year to push the international community into more action.
The Conservatives on Monday unveiled plans for annual limits for asylum as part of a wider package aimed at reducing immigration.
Refugee charities have attacked the plans, saying genuine refugees could be turned away if the quotas were full.
Mr Hague argued the policy could be part of "compassionate Conservatism".
"A weak and uncontrolled system is open to abuse and it is open to abuse by criminal gangs who are wickedly exploiting the legitimate and understandable aspirations of people to find a better life on another country," he said.
The ex-Tory leader used immigration as a core campaign theme at the last election but said his defeat had been caused by continued public faith in Labour.
He argued the Conservatives certainly could win the next election.
"That background in government popularity and faith that Blair would deliver in the end that I was fighting against in 2001 is not there at all today so the great opportunity is now there for the Conservative Party," he added.
Labour has urged its activists not to be complacent about an election victory and says the Tories would take the UK back to the "failed policies of the past".
The Liberal Democrats say they are now the "authentic opposition" and the Tories cannot win the election.