Negotiations on the UK’s post-Brexit relationship with the EU will start on 3 March, more than a month after the UK’s departure from the bloc, the Guardian can reveal.

As a British minister attended an EU meeting in Brussels for the final time after 47 years of membership of the bloc, sources disclosed that officials led by Michel Barnier and Boris Johnson’s Europe adviser, David Frost, would embark on the vital talks in the first week of March with a challenging 10-month deadline.

The UK is due to leave the EU on Friday at midnight central European time – nearly four years since the referendum.

The prime minister has said he will not extend the transition period past 31 December 2020. Until then, the UK will stay in the single market and customs union.

A leaked internal document from the EU member states, seen by the Guardian, notes that without a deal by the end of December 2020, there will be a “cliff edge” in many areas and “no return to the status quo”.

The former European commission president Jean-Claude Juncker had said the negotiations on the future relationship would start on day one after the UK’s exit but preparations on both sides of the Channel were delayed by the general election.

Chris Pincher, the UK’s minister for Europe and the Americas, said after his general affairs council meeting with peers among the 27 other member states – the last by a British minister in an EU setting – that it was a “historic week” when the “government will deliver on its promise”.

Pincher said the UK was leaving the bloc’s institutions as a “sovereign equal” but that it would not be leaving Europe with which the country had a shared “history, civilisation and values”.

Once the talks on the future relationship start in earnest on 3 March, it will be access to fishing waters and the EU’s demand for a “level playing field” that are likely to pose the biggest obstacles to success.

Johnson is expected to give a speech next week spelling out the British negotiating position.

The EU does not have a zero-tariff, zero-quota, traditional free-trade agreement with any country in the world. Brussels is demanding guarantees that the UK will not steal an unfair competitive advantage. The bloc has staked out the uncompromising position that the current fisheries arrangements should largely continue.

During a visit to Brussels for a meeting of ministers, Amélie de Montchalin, France’s secretary of state for European affairs, said the talks could become complicated if the UK failed to recognise the EU’s red lines.

She said: “For us, if there are no clear guarantees vis-à-vis citizens and businesses. If there is no level playing field or fair conditions, the trade openness of the EU will not be total.

“The degree of openness of EU trade will depend on the level of convergence we reach. So, if Boris Johnson wants a deal in 11 months with zero quotas and zero tariffs, we must have guarantees of zero dumping and therefore of a level playing field.

“It’s a fairly simple negotiation. However, we can make it complicated if we are inconsistent. It is impossible to imagine a completely new trading system in 11 months which would require a different normative framework for each area. It’s not realistic. So we’re going to deal with realistic things.”

Brussels’ opening negotiating position will be adopted by EU ministers at a meeting on 25 February. Before then, the two sides will be in “scheduling and scoping” discussions to prepare for the unprecedented negotiation after the end of the UK’s 45 years of EU membership.

A senior EU official said the bloc “will be tough on a level playing field”, adding: “We will not budge.” “We might have a conversation about how we keep to a minimum level of standards but we will not move on the need to have them,” the source said.

The final political act in the UK’s exit from the EU will take place on Wednesday evening when the European parliament is due to ratify the withdrawal agreement.