"It's actually not unhelpful from New Zealand's point of view because we get some informal time to talk to ministers and build those bonds and relationships. In the end, politics is a lot about knowing people and being able to pick up the phone and have a conversation with them. So was it a good use of my time? I'd say yes."
Others at the conference included Australian political campaign strategist Lynton Crosby, from Crosby Textor, which has done work for the National Party. Mr Key said he did not know Mr Crosby well, had not seen his presentation but had spoken to him briefly.
"I just generally said hello and what he's doing over here, it wasn't a very detailed conversation." He said Mr Crosby was not involved in New Zealand politics - he tended to focus on Europe.
Mr Key then moved on to meet with Mr Miliband at Westminster - his first meeting with the Labour leader who is currently beating the Conservatives in the polls and hopes to be Prime Minister after the 2015 elections.
Despite Mr Key's previous engagement, Mr Miliband managed to put tribal politics aside. Speaking to media after the meeting, Mr Miliband began with a compliment for Mr Key when asked why he had wanted to meet with him.
"He's a pretty successful Prime Minister. I was just remarking he ws becoming one of the longest serving leaders round the world, so it's very good to meet him."
He said such meetings were important because of the longstanding relationship between the two countries.
"It's a relationship I value, that I would want to continue if I was Prime Minister. We have people from Britain living in New Zealand and people from New Zealand living in this country, so you are most welcome.
If we could further the relationship between our two countries then I'd be glad to do so."
He would not say if that extended to restoring migration conditions for skilled New Zealanders, which were restricted by changes in 2010. Mr Miliband said Mr Key had raised it with him, and he acknowledged it was important for New Zealand,
"We've got to strike a balance in these things, but I think the most important point I would make is people from New Zealand play a really important role here in Britain and we really value that."
The last politician from New Zealand to visit Mr Miliband was former Labour leader David Shearer, who visited in April and stood down as leader in August. Mr Miliband laughed when he was asked if he was worried he would also be a jinx to Mr Key's political career.
"We aren't from the same political parties, but I think we can both have many issues where we can work together either in Opposition, or, I hope, in Government. It's about the strength of the relationship between the two countries and that's why it's been such a pleasure to meet the PM today."
After meeting with Mr Miliband, Mr Key spoke to a group of tourism sector businesses which specialise in luxury-end tourism before going to a private dinner hosted by High Commissioner Sir Lockwood Smith.
There were plans for the America's Cup racing to be screened for those at the dinner.
