Prime minister says Scottish National party seems to want 'never-endum' rather than referendum on independent Scotland

David Cameron has accused the Scottish first minister, Alex Salmond, of being reluctant to call a referendum on Scottish independence.

Speaking at prime minister's questions on Wednesday, Cameron said that he passionately believed in the union and that the United Kingdom was stronger together than apart.

He told MPs: "I sometimes think when I listen to [the SNP] that it is not a referendum they want, it's a never-endum … I passionately believe in the future of our United Kingdom. I passionately believe we are stronger together rather than breaking apart."

The prime minister said too many people in the Scottish National party were happy to talk about the process rather than the substance of the issue.

Downing Street confirmed that Cameron would be personally involved in talks about the timing and scope of the referendum in the coming week.

Ed Miliband said pro-union politicians should start focusing on the issues at stake. "We on this side of the House believe the United Kingdom benefits the people of Scotland and the people of the rest of the United Kingdom in equal measure," the Labour leader said. "We are stronger together and weaker apart." Both were responding to Salmond's claim that Cameron's determination to force an early referendum on independence for Scotland would increase support for leaving the United Kingdom.

The SNP leader said the prime minister had no mandate to set the rules for an independence referendum, describing Cameron as "almost Thatcheresque".

He added, however, that a deal on how the poll was conducted could be struck.

Speaking on BBC Radio 4's Today programme on Wednesday, a day after the government in Edinburgh insisted it would organise the referendum in autumn 2014 – 700 years after the battle of Bannockburn – Salmond blamed Cameron for inflaming the growing constitutional crisis by starting to pull strings and set conditions.

"I thought his intervention at the weekend was almost Thatcheresque in its nature – the idea that London knows best and it is operating in our best interests but wanting to set the ground rules for our referendum despite the fact it has got no mandate whatsoever for doing so," he said.

Asked whether his government would put only a yes/no question on the ballot paper, as Cameron wanted, Salmond said the legitimate view of people who wanted greater devolution should not be ruled out at this stage.

The attitude of ministers in London had changed significantly recently, he said, adding: "It was not the language they were using, the language of respect, when the SNP won a huge majority in last year's election."

Salmond insisted he was "always constructive about these things" and indicated that a deal could be struck. He said: "As long as it is recognised that [there is a] mandate of the Scottish parliament to organise and hold a referendum – it must be a referendum built in Scotland and decided by the Scottish people – as long as that is recognised, I'm sure politicians north and south of the border are capable of coming to an agreement some time this year about the ground rules for such a poll, and certainly that will be my attitude."

The former Labour chancellor Alistair Darling, also speaking on the Today programme, said Labour must work with Liberal Democrats and Conservatives if those wanting to save the union with Scotland were to be successful.

"Let's be clear – the only reason we have been put off until 2014 is because Alex Salmond doesn't think he can win just now and he is playing for time," he said.

"What currency we will have? Alex Salmond, after all these years in politics, still can't tell us that. Would we be going into the euro with all the strictures they are now visiting on members, how much debt are we going to have, how do we see Scotland's future? These are the big arguments that we need to engage in, " Darling, the MP for Edinburgh South West, said.

"Get the process sorted out, let us get on to the merits of the argument because the sooner we treat people in Scotland like the grownups we are and we have a proper discussion about that, the better it will be."

And the former Liberal Democrat leader Sir Menzies Campbell told the programme: "Remember this – independence isn't just for Christmas. This is asking people to make a decision to bring to an end 300 years of constitutional arrangements.

"There is an important distinction between a political mandate and lawful authority, legality, and it seems to me that it would be very, very difficult and quite wrong for these constitutional issues to become embroiled in legality as to how we make that decision."