A Tory MP is calling for a change in the law after it emerged police routinely told illegal migrants to make their own way to an immigration centre.
Most stowaways are found in the South of England
The government says it has issued new guidelines to police and immigration officials to end the practice.
But Kettering MP Philip Hollobone said officials should be prevented by law from letting asylum seekers go.
He said it was a "national disgrace" that people smuggled into the UK in lorries had been routinely released.
"In the space of less than a week in the middle of September, there were two nonsensical cases in which illegal immigrants were released to do whatever they liked illegally in this country," he told MPs in a Westminster Hall debate on Wednesday.
In one case, three Iraqi migrants were apprehended by Northamptonshire police after a group of 16 jumped from a lorry.
They were released on advice from the Borders and Immigration Agency and told to "make their own way to the immigration offices in Croydon", said Mr Hollobone.
In another case, a group of African immigrants found hiding in the back of a lorry were dropped off by police at a railway station and told to make their way to the same immigration centre.
Police Federation chairman Jan Berry told MPs earlier this month this was "an accurate description of what is taking place in many areas of the country," said Mr Hollobone.
He added: "That is a national disgrace, to be quite blunt, and the government must act and act soon to stop it from happening again."
Junior home office minister Meg Hillier, responding for the government, said it was introducing a range of measures to tighten border controls, including ID cards and watch lists, and procedures on so-called "lorry drops" had been tightened-up.
She told MPs: "The police should not have released those who were released, and we have ensured that that will not happen again.
"The senior management at the Border and Immigration Agency have underlined to the regional directors who are now in place up and down the country - including for Northamptonshire - the need to treat so-called "lorry drops" as an operational priority. That advice is effective immediately.
"The new directors are meeting chief constables from across the country to ensure that there is proper co-operation with the police, and the Home Office is working centrally with the Association of Chief Police Officers to make sure that there is buy-in nationally from the police."
She said most "lorry drops" happen in London and the south east of England and "in those areas, we have established mechanisms for responding to arrests within four hours in most cases, so that police cells are not filled up with illegal migrants".
She said mobile detention vans currently being trialled in Poole, Dorset, may be extended to inland areas such as Northamptonshire, which is on the main road freight route from mainland Europe.
The vans allow illegal immigrants to be held for up to 12 hours while their cases are checked and processed.
But Mr Hollobone told the BBC News website he would still be pressing for a change in the law to impose a "duty on the Border and Immigration Agency to ensure these people are not let go".
He has tabled an amendment to the Criminal Justice and Immigration Bill, which is currently passing through Parliament.