The current UK government was also elected by democratic vote, so they have a mandate that postdates the referendum.
You can argue their mandate is invalid due to the first-past-the-post system, but in that case the original decision to hold a referendum, and all subsequent governments that negotiated the terms of the EU exit are also invalid, since they all derived from first-past-the-post elections.
You can argue their mandate is invalid due to the first-past-the-post system, but in that case the original decision to hold a referendum, and all subsequent governments that negotiated the terms of the EU exit are also invalid, since they all derived from first-past-the-post elections.