As told to Anoosh Chakelian.

The Conservative party is deeply divided on the subject of Europe, and I don't see a short-term resolution to that position. I just reread the speech that the Prime Minister made to the Institute of Mechanical Engineers before the referendum. It was thoughtful, careful, balanced, and highly persuasive – arguing that we should remain in Europe.

A few weeks later, Brexit is Brexit. She has apparently changed her mind, and people like me have not. The idea that the intellectual conviction of the last 70 years of Conservative leadership on this subject can be flip-flopped is asking too much of those of us who believe that our self-interest as a nation is inextricably interwoven with our European allies.

I believe that this is the worst peacetime decision that Parliament has been asked to make. It is very possible, as the negotiations unfold, that members of the Conservative Party in the House of Commons who believe as strongly as I do in the Remain argument will feel that their commitment to our national self-interest is being stretched unacceptably.

I know all the lonelinesses of their position. I'm well aware of the herd instinct of party politics. Only on two significant occasions have I worked to change the official policies of the Conservative party. I have no regrets, it didn't actually do me any harm. They have to evaluate the nature of the decision they're being asked to take.

I don't believe any of the arguments that there's a two-year time scale, the guillotine comes down. If there's a will to change within the community of European leaders, change will happen regardless of the letter of the law.

I believe that there needs to be a second referendum or a mandate of a general election. I believe the sovereignty of this country is enshrined in the House of Commons, and that they must be involved in the final decision with absolute power to determine the outcome. It took Nicola Sturgeon a matter of months to be back on the trail of a second referendum and Nigel Farage would have been doing exactly the same if he had lost. So what is sauce for the goose is sauce for the gander. I cast myself in the unlikely role of gander.

[May’s opposition to a Scottish referendum] completely undermines the whole basis for supporting the referendum judgement in the first place, because they weren't in possession of the facts, and so when we are in possession of the facts, it follows there must be a second choice.

Michael Heseltine is a Conservative peer and a former deputy prime minister.