Thieves who target wealthy department stores should get lighter sentences than if they steal from a corner shop, a senior Labour MP claims today.

David Lammy, an ex-Government minister and barrister, said the likes of luxury goods shop Fortnum and Mason could more easily absorb the loss.

The London mayoral candidate wants the law to be changed so the seriousness of shoplifting is decided by the impact on the victim – rather than the monetary value of the item stolen.

But Tory London Mayor Boris Johnson today condemned the 'absurd' idea, insisting it was wrong to 'minimise shoplifting from swish, posh shops'.

London Mayoral hopeful David Lammy says thieves who target wealthy department stores should get lighter sentences than if they steal from a corner shop

Experts also warned it would make shoplifters more likely to target supermarkets.

Justice Secretary Chris Grayling said: ‘Labour’s justice policies are pretty thin on the ground at the best of times, but this latest contribution hardly seems a sensible one.

‘All forms of stealing are wrong – and suggesting that some people are better able to afford being the victim of it sends all the wrong sorts of messages.’

Mr Johnson branded Mr Lammy's comments ‘absurd’.

The impact of a £150 theft would be far greater on an independent corner shop than on Fortnum & Mason David Lammy MP

He told LBC radio: 'If he is seriously saying that we should discount or minimise shoplifting from swish, posh shops then I think he is totally wrong because it is a crime wherever it is committed.

'It’s important to crack down on it. Tesco’s have got oodles of money – or actually slightly less than they used to – but it doesn’t mean it’s right to nick stuff from anywhere.

'That’s why we are cracking down on burglary and shoplifting.'

Currently, the law decides what constitutes a ‘serious’ shoplifting offence on the basis of an item’s value.

In a pamphlet for the Policy Exchange think-tank, Tottenham MP Mr Lammy says: ‘The impact of a £150 theft, for example, would be far greater on an independent corner shop than on Fortnum & Mason, yet this is not reflected under the current Act.

‘It is self-evident that the impact of a £200 theft to a large retailer is much smaller that it would be to a small, independent retailer.

'Many rightly argue that the seriousness of shoplifting should not be based on the value, but on the impact to the victim.’

Less impact: The London mayoral candidate believes thieves should receive more lenient punishments for stealing from stores such as Fortnum & Mason than from corner shops

Tory London Mayor Boris Johnson today condemned the 'absurd' idea, insisting it was wrong to 'minimise shoplifting from swish, posh shops'.

The idea will prove hugely controversial as, for the first time, it would make the wealth of the victim a factor in deciding sentencing. Critics warn it is a slippery slope which might lead to other crimes – such as burglary – being added to the list.

But Mr Lammy, whose constituency was hit by rioting in 2011, insists: ‘As with most types of property crime, the social costs of shoplifting are regressive – they hit poorest communities hardest.

Mr Lammy's idea will prove hugely controversial as, for the first time, it would make the wealth of the victim a factor in deciding sentencing

‘Small local businesses in more deprived areas, operating on small profit/loss margins, are least able to absorb the costs of theft and are obliged to pass these costs on to their customers through increased prices.’

David Green, a criminologist and director of the Civitas think-tank, said: ‘What any sensible legal system is doing is weighing up the degree of moral responsibility of the person who perpetrated the act.

‘It is completely wrong to punish someone more severely because they stole from a poor person than if they stole from a supermarket.

‘It would encourage people to steal from supermarkets rather than elsewhere because they would know they would get a lighter sentence.’

Mr Lammy’s Policy Exchange report, which will be launched at a speech in London today, warns the police and the courts are turning a blind eye to property crime. Some one in three burglaries and nine in ten shoplifting incidents are not reported to the police because the victims have no faith the case will be properly dealt with.

John Munroe, of the British Retail Consortium, said: ‘Any suggestion a crime against a retailer or staff should be treated any differently because of the type of store, or the place it’s in, is absolutely nonsensical.

‘Retailers are at the heart of every community, whether that’s a high-end shop in Knightsbridge or one in David Lammy’s constituency of Tottenham.

‘Crimes against them are not victimless, they have a direct impact on the local community. Wherever the crime takes place, shoplifters should be persecuted as they normally would be.’

Shoplifting has been repeatedly downgraded in seriousness by the authorities over the past decade.