Northern Ireland will remain the 'open back door' for travellers arriving to the island of Ireland from Britain - despite a new range of restrictions.
Individuals travelling to the Republic from Britain can avoid the new PCR testing regime by taking a plane or ferry to Northern Ireland and then travelling south.
If they are travelling directly to the Republic, they will be required to provide evidence of a negative test.
In a second anomaly, although the Republic of Ireland is requiring negative Covid-19 tests from all passengers on British flights and ferries, the British government is exempting Irish travellers arriving to British ports and airports from any such requirements.
From next week, international arrivals to England, including British nationals, will be required to present a negative Covid-19 test taken up to 72 hours prior to departure.
The procedure will be at the passenger's expense.
It will not apply to arrivals from the Republic of Ireland.
Passengers from Northern Ireland airports and ports are considered part of the UK internal travel system.
Under plans set out by Britain's transport minister Grant Shapps, from next week passengers arriving by boat, train or plane will have to take a test up to 72 hours before leaving the country of departure.
He said the move was designed to prevent new variants of the disease which have emerged in countries such as South Africa and Denmark.
Failure to comply with the new regulations will lead to an immediate £500 fine. "The UK Border Force will conduct spot checks on arrival into England to ensure that passengers are fully compliant," said Mr Shapps.
While the announcement only covers England, ministers were said to be working closely with the devolved administrations on similar measures for Scotland, Wales and Northern Ireland.
Today, Stormont Health Minister Robin Swann confirmed: "I have agreed in principle to the proposed pre-departure testing regime for Northern Ireland."
The move follows the decision to suspend all direct travel to the UK from South Africa following the emergence there of a new strain of coronavirus thought potentially to be even more virulent than the mutant variant from southeast England.
Also today, Foreign Affairs Minister Simon Coveney gave details of an urgent travel advisory for Irish people heading for Germany.
He said on Twitter that "from 8 January, all air passengers from Ireland to Germany, with the exception of those under six, must produce a negative Covid test result less than 48 hours old before boarding the plane."
URGENT TRAVEL ADVISORY— IrelandEmbassyBerlin (@irlembberlin) January 7, 2021
From 08 January, all air passengers from Ireland to Germany with the exception of those under 6 must produce a negative COVID test result less than 48 hours old before boarding the plane.
Intending travellers are advised to contact their carrier pic.twitter.com/S6imdKvZK6
Similar requirements may be introduced for Irish travellers to other destinations as Ireland continues to report high incidence of the Covid-19 and a high R (reproduction) rate.
Meanwhile, Britain's medical regulator approved Moderna's Covid-19 vaccine for use, the health ministry said, adding that it had agreed to purchase an additional 10 million doses of the shot.
Britain now has 17 million doses of Moderna's vaccine on order, and supplies will begin to be delivered to the UK from spring.
Additional reporting: PA