It has always been a Brexiteer illusion that the country can leave the European Union treaties while selecting to retain all the benefits that we enjoy under the treaties and repudiating most, if not all, of the obligations. We have to face up to the fact that that is an illusion. Does my right hon. Friend the Prime Minister agree that the biggest single economic benefit—in fact most of the main economic benefits—that we have enjoyed from our membership over the last decades flow from the completely open border between the whole of the United Kingdom and the rest of the European Union and that upon that have been based huge flows of inward investment, the creation of just-in-time lines of supply and very many thousands of jobs in this country? So will she undertake that we will not change the present basis of that, which is the single market and the customs union, until we know what we are changing to and until we are satisfied that any change will retain those benefits and keep us completely open from any delays and costs caused by regulatory differences or anything else that would be created by moving away from where we are now? The economic future of this country will be threatened very considerably if we just decide, unilaterally, to walk out, as some of my colleagues seem prepared to recommend.