Having different time zones in Dublin and Belfast after Brexit continues to be staunchly opposed by both Britain and Ireland, the minister responsible has confirmed.
The European Parliament voted in March in support of a proposal that would put an end to the twice-yearly changing of the clocks to accommodate extra daylight hours.
Britons - along with the rest of Europe - will wind their clocks back an hour this weekend to revert to Greenwich Mean Time (GMT) for the winter months.
But if the EU adopts so-called "double summer time", then Northern Ireland could be in a different time zone to Ireland for six months of the year after Brexit.
Business minister Kelly Tolhurst said Westminster and Dublin were "united" in their opposition to the switch.
The Tory minister told the EU internal market sub-committee: "We are very pleased the Irish government is with us opposing this. This is something we don't want to happen.
"We are working with our Irish counterparts, particularly with our Northern Ireland Office, to make sure we are presenting a united front on our wishes for this need to happen.
"We are trying to work to make sure this does not become an EU directive.
"Anything that would create a time border in Northern Ireland we are completely opposed to and so is the Irish government."
Irish ministers carried out a public consultation on Brussels' summer time proposals in 2018 but the UK has yet to do the same thing.
The Rochester MP told peers: "Just because we haven't started a formal consultation, it does not mean to say we aren't engaging and listening to people."
She said the Government would look at the policy "extremely seriously" once a "timetable became clear" for its implementation.
The Scottish Government has also voiced its disapproval of any move to "double summer time".
A trial of the concept in the 1970s found deaths on the roads increased during the dark mornings.
Meanwhile, former health secretary and committee member Lord Andrew Lansley raised concerns that the UK would be forced to adopt the policy against its will if the clock rollback was scrapped in the next 14 months.
Once Britain has finalised its divorce with Brussels - a moment that is still pending following MPs' defeat of Boris Johnson's three-day timetable to force through the Withdrawal Agreement Bill - it will remain in a transition period until December 2020 where the country will abide by EU laws, including new ones, without having a say on them.
Ms Tolhurst said she thought it would be "very surprising" if the double-summer policy came "into force next year" while Britain was still in the process of quitting the EU.
The implementation of the suggested change had been held up, the junior minister said, due to member states asking to see an impact assessment from the European Commission.
The proposal to scrap the bi-annual time-switch across the Continent derived from a citizens' forum carried out by the EU.
Under an EU directive, all 28 states currently switch to summer time on the last Sunday of March and back to winter time on the last Sunday of October.