John Key to meet departing British PM David Cameron in London

John Key (right) meets Britain's Prime Minister David Cameron outside 10 Downing Street in 2013. Photo / Claire Trevett

Prime Minister John Key will meet outgoing British Prime Minister David Cameron in London next week.

The informal meeting will be in advance of a trip to Europe which includes a special invitation for the New Zealand Defence Force to take part in a Bastille Day parade in Paris.

Mr Key's visit to Italy and France was scheduled well ahead of Britain's vote on June 23 to leave Europe.

But since then he has managed to get an informal meeting with Mr Cameron added to his trip and seeks one with the European Union.

"New Zealand has strong relationships with both the EU and the UK and it is important that we reinforce both relationships now that Britain's referendum decision has been made," Mr Key said.

The EU is seeking the consent of its 28 (27 without UK) members to begin free-trade talks with New Zealand next year, although it is not clear how distracted the European body will be in negotiating a new relationship with Britain.

New Zealand has also offered Britain assistance in beefing up its trade negotiating capacity which for the past 43 years has been left to the EU.

Mr Key and Mr Cameron have been friends for many years, and the Prime Minister spoke with his British counterpart last week after the Brexit vote and his resignation.

Mr Key will go to Italy to hold talks with Prime Minister Matteo Renzi before heading to France for talks with Prime Minister Manuel Valls, who was in New Zealand in May, and President Francois Hollande.

"I am looking forward to discussing how we can further strengthen those relationships in light of Britain's decision to leave the European Union," Mr Key said.

Other issues on the agenda would include the global economy and counter-terrorism.

New Zealand, with Australia, has received a special invitation to take part in Bastille Day events, which this year coincide with the 100th anniversary of the Battle of the Somme.

More than 80 New Zealand Defence Force personnel will march in the parade.

After the trip to Europe, Mr Key will fly to Indonesia for talks with President Joko Widodo.

Trade Minister Todd McClay and a business delegation will join the Indonesia leg of the trip.