Nicola Sturgeon has suggested Theresa May, in part, called an early general election before allegations over expenses fraud during the 2015 campaign “caught up” with the party.

Ms Sturgeon, the Scottish First Minister and SNP leader, added that “we should not allow the the Tory party to escape the accountability for any misdemeanours that may have led to them buying the last general election.”

In a speech at the Scottish Trade Union Congress, Ms Sturgeon said: “We are, of course, at the start of a general election campaign.

“A campaign called by the Prime Minister last week for one purpose and one purpose only: to strengthen the grip of the Tory party and crush dissent and opposition, and to do so before possible criminal prosecutions for alleged expenses fraud at the last general election catches up with her.”

It comes after 14 police forces sent files to the Crown Prosecution Service relating to the Conservatives 2015 “battle bus” scheme, which it has been alleged led to party candidates breaking strict spending limits on elections.

Last week a spokesperson for the CPS told The Independent that any charges would have to be made before the date of the general election on 8 June. Channel 4 News added that the CPS is considering prosecution against more than 30 individuals with regards to 2015 election expenses.

Police forces who have sent files to the CPS relating to the spending allegations include Avon and Somerset, Cumbria, Derbyshire, Devon and Cornwall, Gloucestershire, Greater Manchester, Lincolnshire, the Metropolitan, Northamptonshire, Nottinghamshire and West Yorkshire.

Ms Sturgeon added that the Conservative vision for the future of the country “should be ringing alarm bells loudly and clearly across Scotland right now”.

She said: “Because, make no mistake, and I think it’s obvious to see, the hardliners have taken over the Tory party and now those Tory hardliners want to take over the country as well.

“It’s no surprise that Ukip right now is losing support to the Tories because the Tories are now threatening to take the UK in a direction that a few years ago Ukip could only have dreamed about, but it should alarm all of us.