LONDON (Reuters) - The chief executive of Britain's Whitbread said the time was right to spin-off the group's Costa Coffee chain from its Premier Inn unit as both businesses were big enough and had international growth potential to enable them to thrive alone.

"We've been delivering a three point plan to make sure Premier Inn and Costa have the right scale strength and capability to survive and thrive as successful independent companies and we've made an awful lot of progress," Alison Brittain told the BBC on Wednesday.

"It's been also important to make sure that we had an international growth story for both businesses before they separate."

She dismissed suggestions that activist investors who had recently joined the company's shareholder list were behind the timing of the divestment.

"If only it had been around as an issue or debate for that short a period," she said.

(Reporting by Sarah Young, editing by James Davey)