Liam Fox has admitted crying with pride as the UK voted to leave the European Union.
The International Trade Secretary and North Somerset MP said the Government had a "duty" to implement the will of voters but refused to guarantee the Brexit process would be completed by the 2020 general election.
Dr Fox insisted the UK would automatically be a member of the World Trade Organisation after leaving the EU and pointed to the US as a country which was able to do business with the European bloc without benefiting from the customs union.
The customs union allows the free movement of goods with no tariffs but imposes administrative and tariff barriers at its external borders.
At a fringe event at the Conservative Party conference, Dr Fox also hinted that he would not put retaining being part of the customs union at the heart of his post-Brexit plans, saying "Most businesses in the world are outside the European Union."
Dr Fox dismissed the suggestion he was advocating a "hard Brexit" with minimal links to the EU.
Dr Fox played a prominent role in the Leave campaign and spoke of his pride at the result.
"I'm sure I wasn't the only one who was really quite tearful... I just felt that given all those big international organisations who had been telling us how bad it would be if we left, I have never actually felt so proud of my fellow countrymen and women as I did at that moment."