Do we have democracy in the UK or a series of dictators who are changed every five years or so?

I think Mrs May is actually very weak. But the formal position on Brexit is perfectly democratic. The previous parliament (elected by the people in our representative democracy) passed legislation that will result in the UK leaving the EU. It is open to the present parliament to repeal or amend that legislation, or to pass new legislation. If it doesn’t, parliament and everyone else must accept the consequences.If parliament merely expresses opinions, the government is perfectly entitled to ignore them. That may or may not be wise, but there is nothing undemocratic about it.