The European Commission will publish its no-deal contingency plans on Wednesday – an attempt to mitigate the damage if the UK crashes out of the EU.
The proposals are designed to limit disruption in certain key areas, such as finance and transport, if Brexit goes ahead in March without a deal.
As PM Theresa May’s proposed exit plan flounders in parliament, both sides are preparing for the worst-case scenario.
The UK has allocated £2bn ($2.5bn) in funding to government departments.
What are the European plans?
The European Commission will set out 14 bare-bones proposals, covering legislation that will aim to ensure some continuity.
The measures address eight sectors, taking in issues such as road transport and customs, and how flights can proceed between the UK and EU.
These areas also include data protection, animal health and plants, climate policy, key financial products and the rights of UK citizens living in the European Union.
Brussels says the arrangements will be strictly time-limited, lasting only for a few months and will be ended without any consultation with the UK.
BBC Europe editor Katya Adler says Brussels will be keen to point out that these proposals are not in the UK’s favour.
They are to protect EU member states from the more catastrophic points of Brexit, if no deal is reached, our correspondent explains.
The European Commission’s initial guidance on the issue was published in November.
It committed to publishing its draft version by the end of 2018, allowing for eight weeks of consultation, as required by EU treaties.
The issue is heating up because Mrs May’s proposed deal, which was agreed with the EU, has so far failed to gain the support from UK politicians, who will vote on it next month.
The deadline for leaving is now 100 days away.
What is the UK doing?
On Tuesday, the cabinet said it had decided to “ramp up” preparations for a no-deal Brexit.
The government has sent letters to 140,000 firms urging them to plan ahead, while 3,500 troops will be put on standby to maintain essential services.
It will also distribute 100-page information packs to businesses on Friday.
The UK is due to leave the EU on 29 March, two years after triggering an EU mechanism known as Article 50, which covers departure from the bloc.