JD1905

I’ve searched high and low, but with different rules in each UK country it is difficult to find a firm answer. Are you allowed to fly domestic from NI to GB at the moment for leisure purposes?

I’m looking to plan a day trip to visit family outdoors in London and return home later that day for personal reasons, so therefore I don’t think i’d be breaking any of the current rules set out by the NI Executive or the PM.

Owenc

There is no rule on this. They can't stop you flying within your country.

noniron

JackDann As Owenc says there is no restriction on domestic flights, EI from BHD and EZ are starting from BFS later this month.

rcspeirs

"There is no rule on this. "
That's not true. The emergency regulations remain in force and they continue to restrict the freedom to travel. There isn't a single rule. Each of the four constituent parts of the UK have their own rules.
I believe that what you want to do is allowed between NI and England but would not be allowed (for example) between NI and Wales.
How will you travel from the airport to where you'll see family? Use of public transport in England is restricted to "essential journeys only" and (within next few days) you'll need to use a face covering.

garykung

I believe essential travel only for now.

NickB

That is not the case. First, there are no restrictions on travel in England which does not involve an overnight stay. What there is is (non-binding) guidance. Second, the guidance does not restrict public transport to essential journeys only. With respect to public transport, the guidance is to try to minimise access to public transport as much as possible by considering alternative forms of transport first and, if taking public transport, preferably traveling at off-peak times.

More broadly, and beyond public transport, the guidance advises to minimise travel as much as possible and to ask oneself whether the journey one plans to make is really necessary. It is plain that a leisure trip of the kind envisaged by the OP is without doubt contrary to the guidance regardless of the use of public transport. However, it is not prohibited by any binding rule.

KARFA

This isn't true in the context of England (i don't know the position for NI, Scotland, and Wales). This has changed since 1 June. Have a look at this post https://www.flyertalk.com/forum/32432985-post600.html

There is no restriction on essential travel as noted by NickB. Neither is there any restriction in law on use of public transport whether generally, or within the context of the new quarantine law in terms of travel between the airport and your designated place of self-isolation.