‘On 18 April 2017, despite previous assertions to the contrary, Theresa May called an early general election for 8 June. The unexpected move was intended to bolster the prime minister’s support in parliament as she leads the UK into Brexit negotiations. The decision also left opposition parties little more than seven weeks to attempt to mount successful campaigns.’
Law Society’s Gazette, 15th May 2017
Source: www.lawgazette.co.uk