Labour MPs have hit out at their party’s “ludicrous confusion” over Tory Brexit policies after being ordered to abstain on the government’s flagship immigration legislation.

Following a severe backlash from backbenchers and other critics, the Opposition embarked on a swift U-turn and whipped its MPs to vote against the Immigration Bill on Monday night.

But the new order was only a one-line whip, effectively allowing MPs to stay away from the Commons vote.

The government won the vote comfortably, with 297 votes for and just 234 against. Only 178 Labour MPs (69% of the total Labour MPs) voted against.

Shadow home secretary Diane Abbott stunned several backbenchers when she revealed that the party would abstain on the second reading of the bill, which sets out curbs on EU migration after Brexit.

Abbott declared that she and other frontbenchers would not oppose the principles of the bill that included the end of ‘free movement’ of EU citizens, pointing out the policy had been included in Labour’s 2017 manifesto.

Abbott was clear that other parts of the legislation would be opposed when the legislation passed through its later stages in Parliament.

Several MPs vowed to break their whip to vote against the proposals, with Chris Leslie and Angela Smith intervening on Abbott to underline their complaints.

Following a hammering on Twitter and ridicule from Labour, SNP and even some Tory MPs, the party then announced a sudden change in its whipping plans.

A text from Labour whips sent to MPs just after 7pm – just three hours before the vote was due at 10pm – read:

“IMPORTANT: Those colleagues who remain on the [Parliamentary] estate may wish to be aware that we will be voting AGAINST the Second Reading of Immigration Bill”.

This contradicted a text – also passed to HuffPost UK – sent hours earlier, which read:

“At second reading we will abstain on the vote, as we accept that a new immigration system is required post-Brexit, but do not support giving the government such wide powers to introduce a new system.

“We will seek substantial amendments in committee stage to restrict the powers granted to the government by itself and require that the immigration system eventually introduced is based on evidence.”

One Labour MP pointed out that this was exactly the reasoning given during Harriet Harman’s decision to abstain on the second reading of the Welfare Bill in 2015. At the time, Jeremy Corbyn was the only leadership candidate to vote against rather than abstain.

The issue flared up during Monday night’s meeting of the Parliamentary Labour Party (PLP), when backbencher Anna McMorrin read out a letter from a party member who was resigning in protest at the decision not to oppose the bill.

One Labour MP said “it’s the biggest fuck-up”, while another said “what kind of half-arsed whip is that?”

“It’s caused ludicrous confusion,” added one usually-loyal backbencher.

A former whip also told HuffPost UK that Abbott’s shadow department was to blame, while others said that ultimately they suspected Corbyn didn’t want to upset MPs in Labour Leave areas who were already nervous about the party’s supporting a delay in Brexit.

“Shadow departmental teams set the policy, not the whips. They would have warned Diane that she faced a problem on this,” the former whip said.

“Her team knew how big it was this morning, but waited until after she’d made a speech in the chamber saying Labour would abstain before changing the position. That is unforgivable and left the whips – and leaves colleagues who now can’t make the vote – in a really tight spot.”

Earlier, Abbott had criticised the bill as “one of the flimsiest pieces of legislation on a major issue that I or many of my colleagues have seen”.  But she also tweeted that “Labour wants to amend Bill substantially. Today isn’t a final vote!”

But MPs made clear they would oppose it.

Tory MP Anna Soubry said she would vote against the bill, while veteran Ken Clarke ridiculed Abbott’s plan to argue against it and then abstain.

“She’s denouncing it from beginning to end, but is saying the opposition don’t intend to vote against it. This makes the proceedings quite absurd.”

The SNP piled in with its own criticism, pointing out that the one-line whip against was still hardly full-blooded opposition.

Some allies of Corbyn pointed out that the party had to balance the different wings of the party, as well as its own manifesto pledge to end free movement.