Eventually, after having driven past the Ballance House between Lisburn and Glenavy hundreds of times I decided to try and find out what exactly it was. Taken from the Ballance House website:
Restored birthplace of John Ballance, 14th Premier of New Zealand.
John Ballance, born in Northern Ireland, was the 14th Premier of New Zealand at the end of the 19th century. He was the founder of the Liberal Party, the country's first organised political party and was instrumental in gaining women the vote.
Interesting house and very tastefully restored, as a visit inside showed.