There will be little official pageantry to mark Britain’s departure from the European Union at 11pm on Friday. A clock counting down the last hour will be projected on to No 10 Downing Street, and Nigel Farage will host a celebration in Parliament Square where flagpoles will fly union jacks.

But there will be nothing like the torchlight procession that marked the august occasion on 1 January 1973 when the prime minister Edward Heath was joined in Brussels by his predecessors Harold Macmillan, Alec Douglas-Home and a chorus of leaders from across the political divide to witness the accession of the UK into the European Economic Community.

Sir Edward Heath signs EEC Treaty of Accession 1 January 1973

Friday will mark the start of what is likely to be an uphill battle to get a trade deal done by the end of the year, not to mention all the non-trade issues that must also be resolved including security and intelligence cooperation, fisheries, data, education and research collaboration.

Does 31 January change anything?

Yes. Although everyday life will remain the same and the UK will remain in the single market and the customs union until the end of the year as part of transition arrangements, the withdrawal agreement will be a legally binding international treaty. It carries sanctions for any “backsliding or half measures”, as Michel Barnier’s adviser Stefaan de Rynck pointed out last week in London.

What happens next?

We know little of the plans for the negotiations, and parliamentary scrutiny of Brexit has been restricted. The House of Lords EU committee has invited but failed to get Stephen Barclay to appear to explain the next stages, sources say.

“The UK is five days away from entering into a highly complex and potentially extensive set of negotiations with the EU, and from entering into quite an elaborate joint institutional architecture with the EU to manage the withdrawal agreement. But we know little in detail about how either of these are going to work on the UK side, in terms of institutions and process,” says Brigid Fowler, a senior researcher with the Hansard Society.

While business has been clamouring for the government to reveal its Brexit vision beyond the joint aspiration of a tariff-free, quota-free deal, little is known about Boris Johnson’s specific goals.

How will the PM lead the next phase?

Johnson is doing everything he can to expunge the word Brexit from the British lexicon. He has already reduced parliamentary scrutiny of the next phase, and his government has given only clues as to what the goals and red lines in negotiations will be.

Negotiating mandates setting out wishlists and red lines are usually published by both sides before they enter into trade talks. Until Sunday, when the Brexit secretary, Stephen Barclay, told the BBC’s Andrew Marr that they would be published, it had not been clear that Johnson would do so at all.

The prime minister is expected to give further clues in a keynote speech in the next fortnight, but parliament’s involvement in approving the negotiating mandate was removed from the Brexit bill.

“Essentially, the government seems to be planning to rely on normal mechanisms for ministerial accountability to parliament. These put the government in control of what information is made public and when,” says Fowler.

What about the cabinet reshuffle and Dominic Cummings’ mooted Whitehall bloodbath?

A reshuffle is expected in early February and some departments are expected to be axed. Barclay’s Brexit department will close on Friday and there could be changes to the function of the Treasury, the Department for International Trade, the Foreign Office, the Department for Business, Energy and Industrial Strategy, the Home Office and the Department for Environment, Food and Rural Affairs.

Michael Gove, the chancellor of the duchy of Lancaster, continues to head a special Exiting the EU operation committee, known as XO, and is expected to continue to have a key role in the next phase.

HMRC will be one of the key cogs in the Brexit chain as work must start urgently on the complex arrangements for Northern Ireland that will affect all businesses trading on both sides of the Irish Sea. Expect an early clash between the EU and Johnson, who has repeatedly claimed there will be no checks on goods, in contradiction of the withdrawal agreement.

New border systems will be needed for the rest of the UK, and the EU and HMRC will be frustrated in designing them until the shape of the deal is known, possibly not until the summer. HMRC is short of key personnel and recently advertised for a deputy director to take charge of EU exit, who “will be responsible for providing the strategic direction for the project, delivering all the operational, communications and business changes needed in readiness for the UK’s exit.”

A former head of HMRC has said it could take five years to get the sort of IT system proposed for Northern Ireland up and running.

When will negotiations begin?

Expect plenty of sabre-rattling on both sides, but negotiations are unlikely to begin before March. The European commission kicked off its 30-stage process in agreeing its negotiating goals before Christmas and these are expected to be signed off by member states at a meeting on 25 February.

Who will be negotiating for the UK?

David Frost, who replaced Oliver Robbins as the chief negotiator, is expected to lead a team of about 30 calling on expert knowledge from civil servants and trade experts. Some have suggested the government should hire as many as possible from the Canadian team that sealed Canada’s new deal with the EU.

What about the joint committee?

Under the withdrawal agreement, a joint committee of EU and UK representatives to oversee implementation of the treaty can sit from 1 February.

While the powers of the committee are known, we know very little else. The appointments process, the size of the committee and how often it will meet has yet to be disclosed. One senior source said the committee would not be as influential as speculated.

What about Northern Ireland?

This remains the single most contentious part of the Brexit deal because of the checks on goods crossing the Irish Sea. De Rynck said last week that the EU and the UK would have to be “very disciplined” if they were to get a new system for trading in Northern Ireland ready for 31 December.

Brussels and Irish political leaders are already alarmed by Johnson’s repeated declarations that there will be no checks on goods crossing the Irish Sea, even though some of these will be mandatory.

Helen McEntee, Ireland’s minister for European affairs contradicted him directly on Sunday telling Sky News’s Sophy Ridge: “There will be no checks on the island of Ireland, we’ve been very clear on this.”

Underneath the joint committee will be a specialised committee and working advisory group to establish the Northern Ireland protocol.

Northern Ireland businesses have urged the government to set up the working group urgently so that the detail of the checks can be determined quickly.