The owner of the Guardian has confirmed it is in talks to sell the Observer, the world's oldest Sunday newspaper, to Tortoise Media.

Tortoise has approached Guardian Media Group (GMG) with an offer to invest around £25m over the next five years on the "editorial and commercial renewal" of the Observer.

Tortoise was launched five years ago by James Harding, a former BBC News chief and a former editor of the Times newspaper.

The Guardian reported that the title will remain a seven-day-a-week digital operation regardless of the outcome of negotiations with Tortoise about the Observer.

Observer staff were told that the investment would "help to safeguard its future" as a standalone product.

Founded in 1791, the Observer is the world's oldest Sunday newspaper.

Mr Harding, editor of Tortoise, said: "We believe passionately in its future – both in print and digital."

He added: "George Orwell described the Observer as 'the enemy of nonsense'. We’re excited to show readers, old and new, that it still is."