The latest measures to be relaxed have also seen primary school pupils in Wales and Scotland return to classrooms, along with some of those in secondary schools.
Children in primaries four to seven have returned to school to join their younger classmates who went back on February 22.
More secondary school pupils also returned to classrooms part-time from Monday.
Up to four people from two households are allowed to meet outdoors in Scotland, as measures on gatherings were relaxed on March 12.
For children aged between 12 and 17, outdoor meetings are also limited to four people, but can be from up to four households.
Communal worship in Scotland will restart from March 26, with the limit for services rising from 20 people to 50.
The stay-at-home order is expected to be lifted from April 5 under the phased plan.
Hairdressers and barbers in Wales reopened for appointments only on Monday.
Primary school pupils also returned to classrooms on Monday, joining those in foundation years who returned in February, and face-to-face teaching will resume for learners in years 11 and 13.
Secondary schools now have the option to bring year 10 and 12 learners back, while there will be “flexibility” to allow all other pupils to “check-in” with teachers on a limited amount of days ahead of a full return after the Easter break.
Meanwhile, all students studying at universities in Wales will be able to return to campus from April 12, the country’s Education Minister Kirsty Williams has said.
The “stay-at-home” restrictions were lifted in Wales on Saturday as the country moved to a “stay local” period, with travel restrictions expected to be eased further in time for Easter.
Four people from two households are now able to meet outdoors to socialise, including in gardens – while outdoor sports facilities, including basketball courts, tennis courts and golf courses, can reopen.
Indoor care home visits are also allowed for single designated visitors.
Non-essential retail will start to reopen gradually from March 22, while restrictions will be lifted on what can be sold in shops which are currently open.
Lockdown restrictions were introduced in Northern Ireland on December 26 and were extended to April 1 by the Stormont Executive, with a review due on March 16.
Thousands of P1 to P3s returned to school on Monday, while nurseries and pre-schools also reopened to all children on Monday.
The next children due back are secondary school pupils in key exam years – year groups 12-14 – on March 22.
The Executive’s plan for gradually exiting lockdown does not include any target dates, with ministers saying decisions on moving between stages will be based on scientific and medical evidence.
All pupils in all year groups returned to classrooms on March 8 with outdoor after-school sports and activities also allowed to restart.
People are now permitted to have socially distanced one-to-one meetings with others outdoors in a public space.
Care home residents are also allowed a single nominated visitor, who will be required to take a Covid test, wear personal protective equipment and keep physical contact to a minimum.
Larger groups will be allowed to gather in parks and gardens from March 29.
The “rule of six” will return, along with new measures allowing two households, totalling no more than six people, to meet.
Outdoor organised sport will also return.
From April 12 at the earliest, shops, hairdressers, nail salons, libraries, outdoor attractions and outdoor hospitality venues such as beer gardens will be allowed to reopen.
Two households, or groups of up to six people, will be allowed to mix indoors and limited crowds will be allowed at sporting events from May 17.
All remaining restrictions on social contact could be lifted from June 21, allowing for larger events to go ahead and nightclubs to reopen.