Wendy Alexander, Labour's leader in the Scottish Parliament, was facing growing internal criticism last night from the party's MPs and MSPs who accused her of attempting to “bounce” them into backing a referendum on independence.

They said that they had not been consulted on the apparent policy U-turn by Ms Alexander who said at the weekend that after “tactical discussions” with Gordon Brown and other senior figures in the party, she wanted to call Alex Salmond's bluff by demanding a referendum as soon as possible and before the SNP leader's preferred date of 2010.

The issue is expected to shoot to the top of the agenda tonight when Scottish Labour MPs meet for their regular monthly meeting at Westminster. Last night John Robertson, secretary of the Labour group of Scottish MPs in the Commons and a fervent supporter of an early referendum, told The Times: “I am surprised by this. This is a U-turn. Although I think this is exactly what we should be doing to shoot Salmond's fox, if Wendy has done this off her own bat, that is not a good thing.”

Meanwhile, Ms Alexander's camp insisted that her hand had been forced by being asked on television about an article in a Sunday tabloid newspaper claiming that she and Gordon Brown were considering the U-turn. Sources close to her also said that she had held extensive consultations with senior Labour figures and that many of them there saw merit in supporting an independence referendum.

In a statement, her spokesman said: “A tipping point has been reached and it is now clear that the General Election will not take place for some time. So there is a window of opportunity in 2009 and it is not in Scotland's interests to delay.”

Ms Alexander's spokesman also cited other reasons for the change of heart. Mr Salmond had “upped the ante” with a recent call for a multioption referendum using the single transferrable vote which could theoretically see Scotland becoming independent with a minority of Scots backing the idea; business leaders had expressed a desire for a referendum to end the uncertainly which was debilitating for the Scottish economy; polls suggested that Scots wanted a referendum; and a special commission to examine the powers of the devolved Parliament in Edinburgh was now up and running. “Alex Salmond wants to delay a referendum because he knows the SNP cannot win it. Wendy believes the uncertainty is bad for Scotland,” added the spokesman.

However, this explanation did not still the criticism from sections of her own party. One senior Labour MP said that at the meeting at Westminster tonight it would be interesting to discover how many of them had been asked for their opinion on the change of tack.

He added: “Wendy forgets that she is not the leader of Scottish Labour. Gordon Brown is. She is only the leader of the Labour MSPs at Holyrood.

“This decision is an indication of her desperation given her own poll ratings. It is almost as if we are always tail-ending and following Salmond. Surely there are more important issues than this for Labour. Who exactly has she consulted on this?”

One of her own MSPs at Holyrood described the timing of the referendum disclosure as “unfortunate”. He added: “One of the problems for her here is that we have a process for discussion within the party. She seems to be launching policy on the hoof.”

It is believed that Mr Brown is still undecided about an early referendum, which senior party figures said suggested that Ms Alexander had decided unilaterally to publicise the possible policy shift.