This month the phoney war over Euro membership will get slightly more real. The Electoral Commission is to issue guidance for groups wanting to register as official “campaigners” in the Brexit referendum, and an outline of the rules.

We know the Conservative party will not register, remaining officially neutral. Labour will officially campaign to stay while allowing party members to do otherwise. But the epidemic of fence-sitting cannot swerve the obvious question, the one voters should be urgently asking politicians: what will your party do if a majority of us vote to leave the EU?

For the upcoming referendum to be democratic there need to be two, real and concrete alternatives on offer. The SNP, during the yes campaign in Scotland, at least, had a shadow central bank team in place, a clear timetable and a proposal on currency, laws and natural resource allocation.

With the EU referendum, while Ukip has published its vision for Britain outside Europe, there is no chance Ukip will be in power to enact the result. Barring accidents, it’s the Conservatives who will be in power – yet the party has published no account of what its actions would be should the referendum it has offered go against David Cameron.

We know from the Scottish referendum what tends to happen in such a vacuum: a last-minute flurry of scare tactics and announcements from the Bank of England concerning imminent doom. A coordinated procession of business leaders on to the BBC to declare their withdrawal from Scotland on the morrow of a yes vote. Variations on a theme of capital flight and state insolvency, real and imagined.

Should the “leave” camp come near the mid-40s in the polls, we can expect the same level of panic (an ICM poll in December put it at 41%). It would be more seemly for parties with a serious chance of being in government to spell out what they would do. So what would a Conservative leave plan look like?

The government would come well armed with research into the eventuality of having to leave. Academic studies, combined with those from the Treasury and the Bank of England, make a powerful case for staying in by enumerating the long-term benefits of membership on trade, finance, labour market size and technology transfer.

In October, the Bank of England acknowledged that none of the published studies was adequate, but for the Conservatives they all pose the same problem: how to maintain the openness and dynamism of the UK economy in the face of a Brexit.

Specifically, you would expect a Tory Brexit contingency plan to cover four specifics: how to maintain the cheap-labour economy based on east European migration; how to keep the City as the financial capital of Europe and promote it as an offshore centre; how to sign a fair and equitable free trade agreement with the EU, and how to replace the EU courts and treaties inside a UK constitutional framework moulded around sovereignty shared with Europe.

For the Conservatives, at least, there would be agreement with mainstream economics about the gist of the problem: how to go on benefiting from flexible labour markets while seceding from a single market of 450 million consumers. But there’s been no coherent anti-EU Conservative economic strategy for two generations. So it’s a big ask.

For Labour, the challenges are the opposite. Labour has a strong, if dormant, anti-EU tradition and a front bench that would find it easy to adapt to a Brexit vote, even if the party has campaigned to stay in. State-aid rules, and rules preventing renationalisation, would be gladly abandoned. The ending of free movement would present a chance for the Labour supporters of a UK “green card”. Accepting the City’s loss of financial dominance, and discouraging its re-emergence as a new offshore finance centre for Europe would come naturally to Corbyn. As for the democratic issues, the need to rewrite the UK constitution would trigger a whole series of reforms that Labour favours, including of the House of Lords.

But the economic strategy challenge for Labour would be huge: in a neoliberal world, suddenly cast adrift from a neoliberal continent, what bilateral deals would a leftwing Labour government be able to make? It is one thing to accept that the neo-Keynesian proposals of Corbyn’s advisers – a state investment fund, state-directed innovation, public ownership of transport and energy infrastructure – could promote growth. It’s another question entirely whether they could do so against an EU determined to thwart them.

On top of the economics, both Labour and the Conservatives should be asked to state whether a major voting divergence between Scotland and the rest of the UK, in the event of a leave majority, should trigger a second independence vote.

Once you pose the questions sharply, it becomes clear why the parties are reluctant to answer them. Neither Labour nor Conservative leaderships can envisage running Britain successfully outside Europe. That some Tory ministers are toying with public support for Brexit is not the big story: this will come when one of them spells out a Conservative strategy for a post-EU Britain. That is, not “bilateral trade deals would be nice to have” but a concrete proposal over who to have them with, how and with what diplomatic quid pro quo.

Given the enormous frustration among British voters with Europe, and the distinct possibility that Cameron’s negotiations with Brussels will fail, all Westminster parties are going to have to spell out their contingency plans. For the vote to be truly democratic, this has to be done clearly and soon.

Paul Mason is economics editor of Channel 4 News. @paulmasonnews