In order to change the US Constitution a a two-thirds supermajority vote is Required.
How to Amend the US Constitution
For the UK government to call a snap general election.
First, the House of Commons can vote for one – but the number of votes for must be equal to or greater than two thirds of the number of seats in the House (including vacant seats).
http://www.markpack.org.uk/28115/how-can-a-general-election-happen/
It Is Not A Mandate 