LONDON (Reuters) - Billionaire John Caudwell, one of the governing Conservative Party's biggest donors before Britain's last national election in 2019, said on Tuesday he would instead be backing Keir Starmer's Labour Party at the upcoming July 4 vote.

"I can declare publicly that I will vote for Labour, and I encourage everybody to do the same," Caudwell said in a statement.

"We need a very strong Labour Government that can take extremely bold decisions and you can rest assured that I will be doing my best to influence them wherever I can, in putting the great back in Britain."

Caudwell made nearly 1.5 billion pounds ($1.9 billion) in 2006 when he sold his mobile phone retailer Phones 4u.

He said he had been despairing about the Conservatives' performance in government for "many years".

Previously, in an interview with Reuters, Caudwell had described Labour as a untested.

Labour leader Starmer welcomed the endorsement.

"I'm delighted that John, someone with such a successful track-record in business, has today thrown his support behind the changed Labour Party that I lead," he said.

"The message is clear: business backs change and economic stability with Labour, and rejects 5 more years of chaos and decline with the Tories."

(Reporting by William James and Elizabeth Piper; Editing by Mark Potter)