How does a second Brexit referendum actually happen?

It was billed as a once-in-a-generation decision, but now the conference season is being dominated by talk of a second referendum or "People's Vote" on Brexit.As of Sunday night, the Labour leadership have caved in to pro-European members and officially put the option on the table, if Theresa May's deal is voted down by Parliament and their preferred option, a general election, isn't granted.Mrs May is expected to secure an agreement - or, less likely, to deliver on her threat to walk away witho