There is still virtually nobody in Brussels who thinks that Brexit is a good idea, for the UK or for the rest of the EU. But decision-makers are now accepting this unpalatable reality and there is a growing impatience for the process to begin in earnest.

There was some understanding for the UK’s desire for a delay in the immediate aftermath of the referendum, recognising that it had carried out no contingency planning for a Leave vote. But now, with a new British government in place, many in Brussels believe it is time for the UK to formulate its goals and formally start divorce proceedings by triggering article 50.

This would require reaching an exit agreement within two years, dealing with the practicalities of leaving and providing an outline of the future UK-EU relationship. It would also need to include transition provisions to bridge the period until such a long-term arrangement is reached, given that those negotiations would take a few years beyond the divorce treaty.

For Brussels, the complexity of long- term choices has boiled down to two broad options for the UK: the Norway model, with access to the single market, but also with obligations in terms of acceptance of EU rules and jurisdiction, financial contributions and free movement of EU citizens, versus the Canada model, a comprehensive trade and investment partnership without these obligations, but outside the single market.

In part, the desire to move on is simply to get this process over and done with as quickly as possible. The UK remains a member state until the point of Brexit, awkwardly still able to co-decide EU policy which will no longer apply on its territory in future. The sheer scope of the Brexit negotiations will clog up decision-making in Brussels.

Post-2017, after the key elections in Germany and France, the EU will need to decide what general direction to take in a post-Brexit world, which will be difficult as long as the UK is still in the club.

There is also a desire to find the final settlement with the UK relatively quickly, to ensure that populists have as little scope as possible to exploit the uncertainty to push for a redefinition of their own country’s relationship with the EU. Only by knowing what “out” really means, can the more pro-European political forces start to construct counter-arguments.

But the EU also needs clarity on the direction of the journey as Brexit will affect a number of EU policy areas, not least those areas related to the EU budget. Given that the UK is a substantial net payer into the EU budget, Brexit might mean renegotiating the whole EU budgetary framework in the next few years. It is due for renewal by 2020 in any case, necessitating decisions on the future direction and size of the budget as early as 2017.

The different options the UK has have very different implications – the Canada option implies no financial contributions, while the Norwegian option would mean a substantial continuing cost to the UK. In fact, given that Britain’s budget rebate would no longer apply, once the UK is out of the EU, Britain could end up paying more to Brussels.

Clarity of the UK position will also be important for the EU’s trade negotiations. It is hard to imagine that countries around the world will be keen to sign up to an agreement with an EU that is changing in an uncertain direction, with the UK in future either still closely economically integrated or outside, with essentially the same status as any other trading partner.

But the EU will have to get used to being in limbo, alongside the UK. Even after article 50 is triggered, it is unlikely that the UK will clearly go for one of the options.

Rather, the UK will want to have the single market cake and eat it: full access but without any of the obligations. And that is not acceptable to the EU. The uncertainty is likely to be long-term.

• Fabian Zuleeg is chief executive of the European Policy Centre