By Michel Rose and Leigh Thomas

PARIS (Reuters) - French Finance Minister Michel Sapin said on Tuesday that Britain's decision to trigger talks to leave the European Union as late as March was a sign London was preparing for tough negotiations, risking a "hard Brexit" not in its interests.

British Prime Minister Theresa May on Sunday announced the end-March deadline, which Sapin said was a late target that gave a signal she was not preparing for easy talks. [nL5N1C80PE]

"It (Britain) has given itself time to prepare for battle, but it would be best to not consider that there is a battle," Sapin said in an interview with Reuters.

"A battle is not in Britain's interest," he said, adding that the 27 remaining members of the EU could be counted on to defend their interests in negotiations.

A French diplomatic source said on Monday that the March deadline helped clarify Britain's intentions and reduce uncertainty lingering since Britons on June 23 decided in June to quit the EU in a shock vote.

Ever since the referendum, the French government has insisted on a quick divorce.

It has also repeatedly warned Britain that it could not expect to retain preferential access to the single EU market, including for London-based banks, if the UK halted the free movement of workers.

Though May has dismissed the idea that Britain faced a choice between a soft or a hard Brexit, many economists and investors fear she will back the latter, where Britain quits the single market in favor of imposing controls on immigration.

"I sensed a certain hardness (in May's position), which is not in Britain's interest," Sapin said in the interview.

"If there is a country that has something to lose from tough negotiations with dire consequences - what's called hard Brexit, it's Britain," Sapin added.

With British banks under threat of losing their right to freely service EU markets from London, France is stepping up efforts to convince banks to set up in Paris.

Sapin is due to meet senior officials from six big U.S. banks over lunch in Washington on Thursday to see what their needs are and explain what France can offer as a city to base their European operations.

(Additional reporting by Yann Le Guernigou and Myriam Rivet; Editing by Ingrid Melander)