Critics say it was improper and in bad taste for prime minister to pose for photos in Slough home after raid by border officials

David Cameron has been criticised for posing for photographs in the home of people suspected of immigration offences as part of a PR stunt aimed at showcasing the coalition's toughness on illegal entrants to the country.

The prime minister was pictured in what appears to have been the kitchen and living room of a home in Slough where four men, thought to be Albanian, were detained by border officials.

His attendance at the raid was attacked by Shami Chakrabarti, the director of Liberty, who said it was at the very least "bad taste and constitutionally inappropriate for elected politicians to intervene in law enforcement".

"Who gave Mr Cameron permission to look round these premises? Being prime minister doesn't give you the right to enter private property willy-nilly," she said. "Are we going to see politicians electioneering by taking part in immigration searches?"

Tom Watson, the Labour MP and former minister, said it seemed "improper for Cameron to be engaging in a PR stunt over alleged illegal immigration before people involved in the raid have been to trial or tribunal.

"They deserve due process and it will be much harder for them to achieve that now that the prime minister has led a media circus to their home," he said. "He was happy to be photographed in the home of the alleged perpetrators. I would like to know whether all the legal requirements were adhered to, including whether his name appeared on the warrant for entry, as is expected in these kinds of raids."

David Cameron and Theresa May speak to Home Office immigration enforcement officers. Photograph: Oli Scarff/PA

Don Flynn, director of the Migrant Rights Network, said it sounded "certainly distasteful" for Cameron to have been there. He said his group had raised questions in the past over media attendance at immigration raids as far back as 2007.

The government has previously been criticised for sending out vans with billboards telling illegal immigrants to "go home or face arrest". The pilot project, which resulted in 11 people leaving Britain, was not extended.

Reports of the visit made by Cameron, who was accompanied by Theresa May, the home secretary, were careful to say that the pair had attended after, rather than during, the raid.

At the time, Cameron tweeted: "Theresa May and I met immigration officers in Slough today after several suspected illegal migrants detained in raid."

David Cameron and Theresa May in what appears to be the kitchen. Photograph: Oli Scarff/PA

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The prime minister said he would make sure migrants from the EU would be able to claim benefits for a maximum of three months, down from six months, unless they had very clear job prospects. The government claimed this would save the taxpayer £500m over the next five years.

But in a sign that all parties are now anxious to be seen as committed to cutting immigration, both Labour and Ukip attacked the prime minister for not going far enough to tackle the issue.

Yvette Cooper, the shadow home secretary, said: "It's almost a year and a half since Labour called for benefit restrictions on new migrants. In that time we've had re-announcement after re-announcement from the Tories, but little in the way of firm action.

"Behind the rhetoric, the true picture of this government on immigration is one of failure, with net migration going up, despite David Cameron's promise to get it down to the tens of thousands."

Cameron has increased his rhetoric against immigration over the past year in an apparent effort to win back voters from Ukip and placate the right of his party. However, the government can do little to stop EU immigration because of free movement rules, meaning it can only embark on repeated efforts to tighten benefits for new arrivals.

The announcement was dismissed as window dressing by the shadow home office minister Lady Smith, and as "vacuous and cynical posturing" by Steven Woolfe, a Ukip immigration spokesman.

Amid criticism of the announcement, Cameron gave an interview threatening illegal immigrants with deportation. "When we find you, and we will find you, we'll make sure you are sent back to the country you came from," he said.

"We are also doing more today to close down bogus student colleges. We've already closed many of them and we will close down more. It's right that the British people know that we have a fair immigration system that says to people: if you're here illegally, you should go home.

"What we're saying is that our changes today will save the British taxpayer half a billion pounds over the next five years, so that is a significant saving. But let's be clear, some people are coming here to work, some people are coming here to claim and some people are coming here pretending to be students.

"I have a very clear approach to this, which is that if you don't have a right to be here, you will be sent home, you shouldn't be here. People want to know that we have a fair, legal migration system, but in terms of illegal migration, we will find you, we will send you home."