Isabel Oakeshott is co-author with Lord Ashcroft of Call Me Dave.

A few days before Christmas, a glossy newsletter arrived on the doormats of prominent business figures across Britain. Amid the deluge of greetings cards and Amazon parcels delivered at the same time, it may have been tempting to overlook the unfestive-looking missive from Eurosceptic campaigners. Those who found time to read it, however, may have been impressed by the long list of names displayed on the front page. All believe Britain would be better off out of Europe.

To City types and those in the Westminster village, they are a familiar bunch: financiers and company bosses; knights and peers of the realm; millionaires and squillionaires. Among them are Sir Rocco Forte, the hotelier; Sir Michael Hintze, the Conservative donor and philanthropist; Lord Bell, Baroness Thatcher’s former election adviser and PR guru; and Robert Hiscox, the insurance grandee.

To those outside the “bubble” however, such folk cut little ice. What the Brexit campaign desperately needs is a “box office” name to front the big push to persuade cautious voters that Britain can thrive outside the Europe club – and contenders for the role now look alarmingly thin on the ground.

As of this week, it appears increasingly unlikely that either of the two big beasts upon whom eurosceptics have been pinning their hopes – Boris Johnson or Theresa May – will throw their weight behind the campaign. Depressingly for those who want the debate to be as exciting and evenly matched as possible, it raises the prospect that a string of grey men (Iain Duncan Smith, Chris Grayling; and Nigel Lawson, among others) will be as starry as it gets for the Leave campaign.

It is a problem that the Remain camp does not share. Britain Stronger in Europe (BSE) boasts both Sir Richard Branson and the Apprentice’s Karren Brady, two telegenic figures who are instantly recognizable and appealing to younger voters and many millions of others who are not naturally inclined to engage with the debate. Both can put a compelling case to wavering voters who instinctively switch off when politicians take centre stage.

Peter Mandelson may be a questionable front-of-camera asset, but the support of three former Prime Ministers as well as the current premier provides all the political ballast BSE needs. Some of those turned off by Tony Blair might listen to Gordon Brown; while yet another cohort retains quiet respect for the view of Sir John Major.

It was probably always too much to hope that a Eurosceptic with equivalent star status to Branson would come forward to make the case for Brexit. For celebrities with meticulously cultivated public images, wading into party politics at all – let alone aligning oneself with some of the divisive characters associated with Brexit – is an unsexy and highly risky career move.

The value of celebrity endorsement in political campaigns is often overestimated in any case. Recent political history is peppered with illustrations of this point. Russell Brand clearly took it too far when he blamed himself for “f**king up the election” last year after Ed Miliband lost despite his endorsement, but the stunt, which saw Miliband visit Brand’s London home to do a 30 minute interview for a YouTube channel, was widely seen to have backfired for both parties.

Similarly, a last minute endorsement for Scottish independence from Wimbledon winner Andy Murray, issued via a breathless Tweet (“Let’s do this!”) on the eve of the 2014 referendum following months of ‘will he won’t he’ speculation, failed to swing it for the SNP.

Yet Eurosceptics do need someone whose appearance on the airwaves does not prompt immediate collective groans– or worse automatic switch off. A string of middle-aged men in boring suits simply will not do.

In alluding to their presentational limitations, I mean no disrespect to Grayling, Duncan Smith and Lawson – three highly experienced, clever political heavyweights who know their subject inside out, and are passionate about the cause. Nor do I mean any slight to UKIP leader Nigel Farage, who has fought for this opportunity all his political life and is an extraordinarily skilful media performer who speaks for swathes of Middle Britain. It will be hard to find anyone who can make the case with as much gusto as he can. All these men be considerable assets to the campaign.

Yet there is a yawning gap for an individual who can take the debate beyond the chattering classes and the Westminster elite: someone with charisma and gravitas, who looks and sounds good on TV and is as recognizable and fired up about the case for leaving Europe as the UKIP leader without being a fraction as divisive.

It’s glaringly obvious who fits the bill: the Mayor of London, one of those rare creatures who is given a hearing by those who dislike politicians and politics. He’s funny, winsome, and has an answer to everything, and if he threw his weight behind Brexit, the prospect of a Leave vote might just be transformed. However, Eurosceptics are increasingly pessimistic that he will join their ranks.

It’s not just that Johnson doesn’t quite know what he thinks, though that is an almighty problem. (“He’s genuinely conflicted,” according to one who knows his mind. “He’s seen the worst of Brussels; there are aspects of it he hates; but he’s also very European in his outlook.”) It is that his approach to the totemic question of Britain’s future in Europe is not governed by what David Cameron this week described as “long standing and sincerely held views” but by calculations about how best to position himself as the next Conservative Party leader.

On the face of it, this political priority points to seizing the opportunity to appeal to the Conservative party membership – who’ll have the final say in the contest to succeed Cameron – by embracing the Eurosceptic cause. After all, the majority of party members are expected to vote leave. (According to ConservativeHome’s most recent poll of party members, 67 per cent back Brexit.) However, for Johnson this critical judgment call is complicated by the question of his next government role.

The Mayor of London already attends political Cabinet as a minister without portfolio.  When he leaves City Hall this spring, he may well be offered a major Whitehall department by the prime minister. He will then face a dilemma: accept the big job, effectively preventing him from leading the ‘out’ campaign; or turn it down to front what may well prove a lost cause. Should he turn down promotion, Cameron will have little reason to give him a second chance – potentially leaving him campaigning for the party leadership from a weakened position, outside cabinet. My impression is that he is squeamish about taking such a huge risk.

Disappointingly, Theresa May appears an even less likely recruit. The Home Secretary may not be exactly box office, but to hear arguments for leaving Europe articulated by one who has experienced first hand the extent to which the UK parliament is hamstrung by Brussels on immigration, human rights and criminal justice would have been powerful indeed. Even better – for novelty factor alone – to have a woman of her status making the case.

Yet I am told she does not really believe in the cause. Her controversial party conference speech last autumn on the perils of mass migration raised hopes that she was positioning herself to embrace Brexit, but I am told her heart is simply not in it.

It remains possible that Sajid Javid, who last year told the Confederation of British Industry that it was wrong to say that the UK should stay in the EU “no matter what” will throw his weight behind the cause, but he too has been sending out mixed messages of late. Intriguing a figure as he is, he is in any case insufficiently high profile to be any kind of star in the show.

This gloomy state of affairs is all the more frustrating when victory does not look hopelessly out of reach. Setting aside the corrosive continuing feud between Vote Leave and, there have been some encouraging signs for eurosceptics of late.

For one thing, evidently money will not be a problem. UKIP may be in dire financial straits, but Vote Leave and are in good shape. Having launched an appeal to wealthy potential backers at the end of last year, seeking ten “Founding Fathers” (no mothers!) to give £1 million each to support what it called “this once in a generation vote,” Vote Leave has now amassed pledges for as much money as it will legally be allowed to spend during the official campaign (£7 million) should it win the official nomination.  I don’t know how much money has raised, but its founder Arron Banks cheerfully says he could bankroll it all himself, if he chose to do so.

Meanwhile, Toyota’s vow this week to remain in the UK even if Britain leaves the EU is a major boost. It should encourage more companies to say the same, making it clear that far less jobs hinge on the outcome of the referendum than ‘Stronger in Europe’ likes to claim.

It is still many weeks before the air war gets underway. Eurosceptics can only hope a saviour is waiting in the wings to front the campaign.