Nick Clegg claimed that Westminster-based media were missing the big story of the European elections – the extent to which Ukip is eating into the traditional Labour northern heartlands in both the local and European elections.

There may be some wistfulness and wishful thinking in this analysis. Clegg at one time wanted the Liberal Democrats to become the challengers to Labour's northern heartlands, and instead he has seen his party pushed back, replaced by Nigel Farage's. Inquests will await the election results, but the Clegg theme chimes with some thinking in the shadow cabinet.

The question of whether Labour did enough to combat Ukip both by reassuring potential Labour voters on immigration and by portraying Farage and his acolytes as rightwing Thatcherites has been bubbling for weeks.

Both the Blue Labour wing – loosely supporters of Jon Cruddas such as Lord Glasman – and some more traditional centre-right Labour figures in the shadow cabinet have urged a stronger attack on Ukip. One shadow cabinet source pointed to a weekend YouGov poll showing that more than 60% of voters admitted they did not know anything about Ukip's policy on the economy, crime, NHS, defence or education. Those figures arguably show how far Farage has been let off the hook, including by the media. Farage himself has made a virtue of refusing to discuss domestic policy.

There is a view that Ukip is almost immune to rational political attack, since it represents a resentment with politics and modern life incapable of being shifted by statistics, reason or rhetoric. Clegg found himself caught out by this during his televised debates with Farage. Equally there is a view that any attack on Ukip has to be carefully calibrated or else it comes across as a patronising misreading of voters' legitimate anger. There is also a third, slightly cynical view in shadow cabinet circles. If Ukip performs at 5%-7% in the general election, that may actually help Labour since the bulk of the Ukip vote will be former Tories.

There is a big debate among pollsters and politicians about whether this holds true. Many potential Ukip voters hold traditionally leftwing views on tax and equality.

There is also a wider issue that unchallenged, Ukip's presence drags the political agenda to the right, making it more difficult to get a hearing for Miliband's solutions to the ills it plays upon.

Miliband has honourably chosen to fight a relatively policy-rich campaign highlighting the issues he believes will resonate with core voters – 48-hour access to GPs, tighter regulation of private sector rents and zero-hours contracts, changes to the way in which social care is delivered, and help for the low paid. Equally, he has long rejected the David Cameron course of appeasing the Eurosceptics, saying he will not offer a definite in-out referendum on the UK's EU membership. He says repeatedly he thinks it will be unlikely that Britain will need to have a referendum on its EU membership in the next parliament.

Labour strategists also point out that Miliband mounted an attack on Farage in a lengthy piece in the Daily Mirror at the outset of the campaign, adding it was always intended that immigration feature in the closing days of the campaign. A recurrent theme since he became leader has been to insist that the free movement of workers, or the limited offer of welfare benefits to EU migrants, must not become a means to exploit the indigenous workforce.

But it is notable that the shadow home secretary, Yvette Cooper, has chosen to go on the offensive claiming that it was Tory and Lib Dem commitment to the free labour market that led the two parties to ignore the impact of immigration and made it possible for Ukip to play on people's fears.

She highlighted the long-running government efforts to thwart and dilute a European commission-led measure to strengthen enforcement of the EU Posted Workers Directive, a set of proposals designed to ensure that when people moved around the EU to work for their employer (posted workers) they got a fair rate of pay for the country where they worked, rather than undercutting the local labour force.

UK employment ministers have for years resisted the enforcement measure, but in March under pressure primarily from the French and Dutch government agreed to let some relatively mild enforcement mechanisms go through.

It is an issue Miliband has raised before, but since each member state now has two years to introduce the enforcement directive, Labour can realistically offer to strengthen how it is implemented in the UK.

Labour wants for instance to introduce joint liability in the construction sector, a measure that would make a construction firm liable if a sub-contractor was using EU laws to underpay its staff on UK sites. It is claimed that companies form "letter-box companies" in countries where taxes and social security contributions are the lowest, and then pay staff according to those rates.

Cooper said "The Tories and Liberal Democrats are doing nothing to stop employers exploiting cheap migrant labour to undercut local wages and jobs. And Ukip would make it worse by taking away employment rights. People are concerned about immigration. And unless the government takes action against dodgy employers and agencies who exploit immigration to undercut jobs and wages, those concerns are going to get worse".