Sellers of legal highs should shut down their operations immediately before a seven year jail term comes into force, the Police Minister has warned.

Mike Penning told MPs the Psychoactive Substances Bill would immediately make selling the drugs illegal as soon as it is passed by Parliament.

Mr Penning dismissed claims the Bill would criminalise innocuous substances such as coffee or netmeg as "tosh" but told MPs a "blanket ban" on so-called legal highs such as "hippy crack" would save lives.

Instead of forcing each new legal high to be individually banned as they are created and sold, the Bill creates sweeping new powers to make all psychoactive substances illegal with listed exceptions.

It bars production, distribution, sale and supply of legal highs.

The Bill enjoys some cross party support but was strongly opposed by the Liberal Democrats in the House of Lords.

Labour's John Mann pressed Mr Penning on how quickly the new laws could be brought into force.

The Minister said: "We want them to close down before this Bill is passed. I want this House to send a message to those that are selling these products... that on the day this gets Royal Assent that will become an offence.

"Saying that, they have been selling these products perfectly legally for many, many years.

"So we need to give them the opportunity. This is only part of a process of educating the public as well as helping people that are addicted to these substances.

"At the end of the day they have to know if they sell these products from the day this gets Royal Assent that is illegal, it is a seven year sentence at the end of this."

Green MP Caroline Lucas (Brighton Pavilion) insisted similar laws were not working effectively in Ireland.

Intervening, she said: "I would ask you if the Irish example and the ban has been so successful, why is it that the lifetime prevalence of the use of novel psychoactive substances among young people there has increased from 16% to 22% in the last three years?"

But Mr Penning rejected the concern, telling MPs: "I don't want any more deaths. If we hold back now and wait for more studies and more this and more that... at the end of the day I am absolutely determined to protect young and old."

He added: "At the end of the day, what are we sent here to do? Protect people and that's what we are going to do this evening."

Lyn Brown, shadow home office minister, stressed that the bill will not "shut down the industry altogether" but by containing the production and supply of such substances "we will hopefully reduce the harms to young people".

She also attacked the shops that sell such substances.

She said: "Our young people think that they are legal and safe because they are literally in front of them in a shop on the high street, therefore if it wasn't legal and safe the police would have come along and nabbed them."

She told the Commons the Bill would send a message to young people "who are unaware these substances are dangerous".

Meanwhile, she also said people need to realise that just because something is described as a legal high that does not mean it is safe.

"This is a dangerous misunderstanding because some of the new psychoactive substances have gone on to be controlled, have been designated as Class A, indicating that they were some of the most harmful drugs around before they were controlled," she said.

"Passing this legislation has the potential to put to bed the dangerous myth that psychoactive substances are safe.

"But it will only do so if it is supported by concerted communication and education strategy."

Ms Brown raised concerns about some elements of the Bill.

She stressed the need for the legislation to differentiate between people who mass import psychoactive substances and those who may buy a smaller amount to share with their friends.