Both official EU referendum campaign groups, Britain Stronger In Europe and Vote Leave, have now appeared in front of the Treasury Select Committee as part of their inquiry into the costs and benefits of the UK’s membership of the EU.

The influential Committee, led by the independent-minded Andrew Tyrie, is considered the ultimate Parliamentary forum for forensic scrutiny of economic data and arguments, and presents a tough test for those seated in the witness’ chair.

For the Stronger In campaign, Lord Rose, the campaign’s Chairman, and Will Straw, Executive Director, gave evidence to the Committee. On behalf of the Leave campaign, Campaign Director Dominic Cummings faced the Committee alone. Matthew Elliot, the campaign’s Chief Executive, should have appeared alongside him but was unable to attend. He has since declined a second session, but will not be able to avoid the Committee for long.

So how did the campaigns fare under the scrutiny of Tyrie and his gang?

Tyrie used both sessions to interrogate the campaigns about their use of figures in their campaign literature. While he accused Lord Rose of a “scandalous misuse of data”, he warned Dominic Cummings of playing “hard and loose” with the facts.

Lord Rose took Tyrie’s comments very personally, accusing Tyrie of challenging his intellectual integrity, but ultimately he was lucky that Will Straw was able to defend the campaign’s positions on their figures more confidently. In comparison, it was to Dominic Cummings detriment that Matthew Elliot dropped out of the session at the last minute. Left to his own devices, Cummings argued that none of the figures in the campaign would withstand “serious scientific scrutiny”, including his own, and resorted to a number of controversial claims such as accusing senior officials in the Cabinet Office and Number 10 as threatening and bribing businesses against coming out for Leave.

As more and more reports come out suggesting a negative economic impact from Brexit, Vote Leave will need more robust rebuttals than simply dismissing all figures. To paraphrase an old saying, you can dismiss some of the experts some of the time, but you can’t dismiss all of the experts all of the time.

HM Treasury analysis shows that under all three alternative models to EU membership (membership of the European Economic Area, allowing free movement of persons, goods, services and capital within the EU’s internal market; a bilateral agreement giving the UK some access to the Single Market, such as Switzerland and Canada; or membership of the World Trade Organisation), the UK’s economic openness and interconnectedness would be reduced, and we would be “permanently poorer”.  Mark Carney, Governor of the Bank of England, has warned that Brexit is the “biggest domestic risk to the UK’s financial stability”. He added that a vote to leave the EU would “reinforce existing vulnerabilities” in the UK economy, including a risk around the UK’s trade deficit. The IMF has warned that Brexit could lead to “severe” damage to the UK and the world economy.

Given his chance by the TSC to refute some of these claims, Cummings chose instead to describe the Treasury report as “snake oil” produced by “charlatans”. When asked if Vote Leave would be putting out their own economic analysis, Cummings gave a vague response about publishing “lots of things” in due course. It remains to be seen if these “things” will amount to a convincing rebuttal.

However, while Cummings’ arguments may have been far-fetched, no one could accuse him of lacking belief in his cause. In comparison, Lord Rose did not exactly come across as a man passionate about EU membership and all it has to offer, which is not entirely surprising as he has himself voiced Eurosceptic sentiments in the past. Despite protestations that they are not running ‘Project Fear’, both Rose and Straw repeatedly emphasised throughout their session that Brexit is a massive unknown and therefore a huge risk. When it comes to positive arguments over why we should stay, these were slightly thinner on the ground.

Having said this, the ‘Project Fear’ approach can be effective, and there is a much documented tendency for undecided voters to gravitate towards the least risky option. To put these arguments to flight, Vote Leave need to convince the electorate that the benefits of Brexit outweigh the risks.

But given his opportunity to do so, Cummings failed to dispel accusations that the Vote Leave campaign lack coherent arguments about what Brexit would actually look like and the benefits it would bring. Instead he argued that the campaign is about more general fundamental principles rather that suggesting individual policies. He did not put forward any specific alternatives to EU membership, saying that this is not a concern as the UK will be doing something new and forging its own path.

By continuing in this manner, Vote Leave offer themselves up to easy criticism from the Remain side. As the referendum date draws closer, Vote Leave need to offer serious suggestions of what life outside the EU will look like, backed up by reliable economic analysis. Without this, they will struggle to persuade undecided voters.

The main challenge for the Remain campaign is to enthuse voters so that they actually turn out on the 23rd June, as a low turnout on the day is likely to give Leave the upper hand.

For the time being, the Remain campaign will probably be content not to have to face Andrew Tyrie again any time soon, but the ordeal is not yet over for Vote Leave.