Across the Irish Sea in about an hour
Farnborough to Dublin is 239 nautical miles, 275 statute miles; Luton is slightly closer, London City and Biggin Hill about 20 nm further. Every cabin flies it in a little over an hour, so the choice of aircraft is about the party and the luggage, not the range.
On the Irish side one airport does almost all the work. Dublin Airport sits about 8 km north of the city centre, and every private passenger goes through Platinum Services, the airport's own private terminal, whichever handler looks after the aircraft. It is the arrival for the city, for Ballsbridge and the Aviva Stadium, and for the country houses and golf of Kildare and Wicklow.
Ireland is outside the EU's passport-free area but inside the Common Travel Area with the UK, so the formalities are lighter than a flight to the continent: an identity check for British and Irish passengers, and the EU's Entry/Exit System does not apply. The paperwork that does take planning is a dog's, and it is set out below.
Which London airport to leave from is set out in our guide to the private jet airports in London: FBOs, customs and curfews, side by side.