Britain on Friday formally told the European Union that it would not seek to extend a post-Brexit transition, raising the prospect of a disorderly split in just six months time.
London and Brussels are racing to agree a new trade deal for when Britain leaves the EU's single market and customs union on December 31, but talks have stalled.
Prime Minister Boris Johnson's government says that even if negotiations fail, it will not take up the option of more time -- a decision that must be made by July 1.
"I formally confirmed the UK will not extend the transition period and the moment for extension has now passed," senior minister Michael Gove tweeted after online talks with EU counterparts.
"On 1 January 2021 we will take back control and regain our political and economic independence."
Meanwhile, it emerged London has abandoned plans for full border checks on goods from the EU after the transition so as to avoid further disruption for businesses affected by the coronavirus outbreak.
New figures showed Britain's economy shrank by more than a fifth in April from March -- a record -- as the first full month of its virus lockdown ravaged activity.
The Financial Times reported that Britain will introduce a temporary "light-touch regime", regardless of whether a new trade deal is agreed.
"These are unprecedented times," Johnson's spokesman said when asked about the report.
"That's why we're putting in place a pragmatic and flexible approach to help businesses adjust to the changes."
Britain formally left the EU on January 31 after 47 years of membership but both sides agreed to a standstill transition in which to agree a new security and trade relationship.
Negotiations have been stuck for months on crucial issues such as fishing rights and commitments to maintain EU standards on health, safety, state aid and the environment.
Johnson himself will get involved next week, speaking to EU Commission president Ursula Von Der Leyen on Monday to assess progress.
The leaders of the devolved governments in Scotland and Wales on Friday called on Johnson in a joint letter to extend the transition period to support businesses.
"We believe that exiting the transition period at the end of the year would be extraordinarily reckless," Scottish First Minister Nicola Sturgeon and Welsh leader Mark Drakeford wrote.
Without an extension, "at very best there will only be a damaging 'bare bones' trade deal or even worse, a disastrous no-deal outcome".
But EU commissioner Maros Sefcovic said Gove "couldn't be clearer" about the British position in their talk Friday.
"This was the last (EU-UK) joint committee before the deadline is expired so we take this decision as a definitive one," he added. He said Brussels was "pleading" for work to be accelerated to secure a "very close and cordial relationship" by the start of 2021.
Brussels on Friday confirmed that the trade talks will continue through the summer months, with negotiating rounds now set for July, August and September.