Britain had a general election in 2017. Labour was unable to unseat the Conservative government then. There is no need for another general election now just because the Labour party does not like the way Brexit is being handled.
At such a critical juncture, as Theresa May concludes Brexit negotiations with Brussels and prepares for a vote in Parliament over the final deal, a general election is out of the question and would harm national interests.
Since the two largest parties are both split over Brexit, a General Election fought on Brexit might be decided on other issues, and could produce another Parliament that doesn’t have a majority for any particular version of Brexit.
Under the Fixed Term parliament Act we can have an extra election either if two-thirds of MPs vote for it, or if the government loses a confidence vote and no-one else wins a confidence vote within two weeks. Neither condition has yet been met.