Britain's Hotel Chocolat agreed to a 534 million pound ($662 million) takeover offer from Mars Inc on Thursday, the specialist chocolatier succumbing to the U.S. food giant with international expansion in mind.

Set up twenty years ago, Hotel Chocolat aimed to make chocolate exciting by bringing ethical affordable luxury to the British high street, and joint founder Angus Thirlwell remains chief executive to this day.

The 375 pence per share recommended cash offer announced on Thursday represents a 170% premium to Hotel Chocolat's share price on day before the offer, and looks set to bring to an end the group's seven years as a listed company.

Hotel Chocolat, with its luxury hotel on its cacao estate in Saint Lucia, chocolate cookbooks and inventive tastes which shunned sugar in favour of cocoa, chimed with consumers in Britain and now has 130 stores across the country, plus a presence in Japan through a partner deal.

But the group posted what it called disappointing results in its last financial year -- its stock has fallen 11% in 2023 so far -- and it said on Thursday expanding overseas would require substantial investment.

Thirlwell, who will stay on with the business under family-owned Mars, said growth would be faster under new ownership.

"We know our brand resonates with consumers overseas, but operational supply chain challenges have held us back. By partnering with Mars, we can grow our international presence much more quickly," he said in a statement.

Thirlwell and co-founder Peter Harris both own 27% of the equity, according to LSEG data.

(Reporting by Sarah Young; Editing by Kate Holton and James Davey)