We need a transitional Brexit deal that provides maximum certainty and stability. Labour will deliver it. If we are to deliver a deal that protects jobs and the economy, we must be clear about the hard choices that need to be made.

Constructive ambiguity – David Davis’s description of the government’s approach – can only take you so far. This has been underlined by the bland and noncommittal policy papers the government has published in the last two weeks.

Labour has repeatedly emphasised that in order to avoid a cliff edge for our economy there will need to be a time-limited transitional period between our exit from the EU and the new lasting relationship we build with our European partners. This is a view shared widely by businesses and trade unions, who recognise the huge damage that an abrupt separation from the EU would cause to our economy.

For a long time any notion of a transitional period was anathema to the prime minister and leading Brexiters in the cabinet. They preferred to labour under the delusion that the incredibly complex process of negotiating and delivering a new relationship with the EU could be delivered within 24 months.

The harsh realities of the negotiating process and the glacial pace of progress in the first two rounds of talks have helped puncture this illusion. There is now near consensus that a transitional period is an economic and political necessity. So I want to be absolutely clear about the type of transitional deal Labour would seek to negotiate. No “constructive ambiguity”. No mixed messages. A credible solution to one of the most important issues facing Britain’s exit from the EU.

Labour would seek a transitional deal that maintains the same basic terms that we currently enjoy with the EU. That means we would seek to remain in a customs union with the EU and within the single market during this period. It means we would abide by the common rules of both.

That is a choice Liam Fox and Philip Hammond explicitly ruled out a fortnight ago, stating that Britain would be outside the customs union and the single market in any transitional phase. Labour rejects that as an unnecessary and highly risky path to take.

By remaining inside a customs union and the single market in a transitional phase we would be certain that goods and services could continue to flow between the EU and the UK without tariffs, customs checks or additional red tape. There would be no need to set up complex alternative customs or trading relations. Given that UK-EU combined import/export trade totalled £553bn last year, this certainty would be hugely advantageous for British businesses and consumers. This arrangement would also safeguard the important social protections and rights that come from being within the single market.

There are a number of other significant advantages to this approach. First, it is a grown-up acknowledgement that bespoke transitional arrangements are highly unlikely to be negotiated, agreed and established in the next 18 months. Second, it provides maximum certainty for businesses and allays concerns that there will be delays or disruptions to trade when we leave the EU in March 2019. It would also ensure there will be a one-step transition to a new final relationship.

Third, it provides more time to resolve the complex question of the Northern Ireland border. Labour is clear that this extremely serious issue must not be rushed and that a considered agreement needs to be reached that prevents a hard border and has support from all communities. The government’s policy paper on this was incredibly light on detail and gave precious little reason to believe this will be resolved satisfactorily by March 2019.

Fourth, it would enable negotiations to focus on the central Brexit issue: the nature of the new partnership that needs to be built between the UK and the EU. This is challenging enough without having to negotiate separate transitional arrangements at the same time.

Labour also recognise that this transitional arrangement would – for all its merits – be imperfect and prove unsustainable beyond a limited period.

It would not provide a durable or acceptable long-term settlement for Britain or the EU. It would not provide certainty for either party. It leaves unresolved some of the central issues the referendum exposed – in particular the need for more effective management of migration, which Labour recognise must be addressed in the final deal.

That is why a transitional period under Labour will be as short as possible, but as long as is necessary. It cannot become a kind of never-ending purgatory. That would simply create its own uncertainty and ambiguity.

Instead, transitional arrangements must be a bridge to a strong and lasting new relationship with the EU – not as members, as partners. That new progressive partnership should be based on our common values and shared history. It must extend far beyond trade and security to include education, science, technology, medicine and culture.

It must be based on a deal that, as Labour made clear in our manifesto, retains the benefits of the customs union and the single market. How that is ultimately achieved is secondary to the outcome.

But the prime minister’s ideological obsession with leaving the customs union and the single market during a transitional period means the options to deliver a good deal for Britain are diminishing fast. The fanciful and unachievable proposals put forward in the government’s recent customs paper show the colossal risks it is willing to take with British jobs and the economy.

Labour will not take those risks. We will always put jobs and the economy first. That means remaining in a form of customs union with the EU is a possible end destination for Labour, but that must be subject to negotiations.

It also means that Labour is flexible as to whether the benefits of the single market are best retained by negotiating a new single market relationship or by working up from a bespoke trade deal.

Those two questions must be central to the Brexit negotiations. The government should not be wasting time pursuing bespoke transitional arrangements when certainty and clarity are what is needed.

Keir Starmer is shadow secretary of state for exiting the EU