"Sir Ivan's warning shouldn't be taken as a great surprise.

"It is folly to expect the UK to just walk into a new free trade agreement with the EU. As the EU's recent trade negotiations attest - with Singapore, Canada, and still ongoing with the US through TTIP - complexity and years of haggling are the order of the day.

"Any EU-UK FTA will have similar issues of complexity, not least if financial services are included, and must therefore be expected to take a considerable amount of time if both the EU and UK want to achieve the best possible deal for both parties."

Dr Megan Dee, Associate Research Fellow, Politics and International Studies