(Adds details, background from paragraph 2) Dec 18 (Reuters) -...

(Adds details, background from paragraph 2)

Dec 18 (Reuters) - Australia's Origin Energy (ORG) on Monday increased its stake in UK-based renewable energy firm Octopus Energy by 3% to 23%, by investing 280 million euros ($305.8 million).

Origin is investing alongside existing major investors Canada Pension Plan Investment Board (CPP) and Generation Investment Management (GIM), it said in a statement.

CPP will invest 300 million euros to raise its stake in Octopus to 11% from 6%, while GIM will invest 45 million euros, maintaining its interest of around 10%.

This latest capital raise is being executed at a pre-money valuation of 5.6 billion euros, which represents a 60% increase in the value of Octopus since December 2021, Origin said.

Octopus is now the UK's second-largest energy retailer and its platform Kraken is contracted to serve over half of UK households and licensed in ten countries, which is critical in a rapidly transforming energy system, Origin CEO Frank Calabria said.

The transaction is subject to investors obtaining required regulatory approvals, with Origin’s additional investment requiring approval from the UK’s Financial Conduct Authority, the company said.

($1 = 0.9155 euros)