* PM has revealed little about Brexit negotiating plans
* Domestic battle with eurosceptics could offer guide
* May took firm stand, refused to give ground to rebels
By Elizabeth Piper
LONDON, March 5 (Reuters) - British Prime Minister Theresa May is unlikely to bow to political expedience in Brexit negotiations but will make up her own mind about what she believes is best and refuse to give ground - that's if past form is anything to go by.
May, who backed the campaign to stay in the European Union in last June's referendum, will have to carry or quell the eurosceptics in her ruling Conservative Party as she formulates her negotiating priorities and strategy.
The 60-year-old - often described as "sphinx-like" in the British press - has revealed little in her first eight months as leader about how she will approach divorce talks with Brussels, perhaps wary of weakening her hand.
But her previous experience of trying to win the support of the eurosceptics who drove Brexit could offer some clues about her modus operandi: two years ago when as interior minister she sought to opt back into the European Arrest Warrant against the wishes of many in her party.
May got her way in the end after a bruising encounter over the warrant, which speeds extradition between member states. She did not backtrack an inch and forced it through parliament.
Her conduct and strategy present a picture of a stubborn negotiator who sticks as firmly as possible to what she believes is in Britain's best interests.
Several government aides and a lawyer with knowledge of the matter said she was driven by a conviction she was right - that Britain needed to adopt the warrant and other EU justice measures - and, while acknowledging their shortcomings, would not let anything stand in her way.
Supporters say her ultimate success offer evidence of her political steel, know-how and negotiating skills. Critics say the self-belief that drove her to open a rift in her party and face down a rebellion could be a weakness if it becomes inflexibility that hinders Britain striking winning the best deal.
"If you believe in what you're doing, that's key. If you do believe you're doing the right thing, that gives you resilience," May told the BBC's Desert Island Discs programme less than two weeks after the fight.
She steadfastly refused to allow lawmakers a vote on the arrest warrant which she said was in "our national interest", reneging on a pledge to the outrage of the eurosceptics, instead offering only a vote on a broader package of justice measures.
In a rare admission that her strategy may have been misjudged, she added in the BBC interview: "If I was starting it again now, would I do it in a different way? Given the understanding of how parliament felt then, perhaps I would."
May spent six years as home secretary, or interior minister, before taking over from David Cameron as prime minister last year following the June 23 referendum when Britons backed leaving the EU by 52 percent to 48 percent.
The premier, who describes herself as "not a showy politician", is something of an anomaly in a porous political scene rife with secret press briefings.
Her closest aides, loyal since she became home secretary in 2010, ensure very little leaks. One government aide called her team "one of the most effective in Westminster".
She has said she will trigger Article 50 of the Lisbon Treaty, launching two years of divorce talks, by the end of this month. Parliament is expected to approve legislation to start the negotiations by mid-March.
She will enter the EU negotiations with a long and broad wish list - wanting the closest possible trading conditions, maintaining security cooperation, regaining control over immigration and restoring sovereignty over British laws.
It is an opening negotiating stance - one British government source, who spoke on condition of anonymity, asked why would anyone start talks with anything less. Another British official said any strategy would evolve, depending on what the EU came up with and how the other 27 member states approached the talks.
But with EU officials balking at granting her a good deal, fearing other European countries might follow suit, May will have to find a path to compromise.
The so-called Brexiteers, or eurosceptic lawmakers in her party, will watch her every step closely as Britain negotiates a deal, to make sure they have scrutiny of all aspects. May will work hard to keep them on side.
"At the moment we have just been negotiating with ourselves," said a veteran politician now in the upper house of parliament. Once Britain starts negotiating with the EU, he said, the "very dysfunctions Brexiteers complained about are the same dysfunctions allowing them or not to arrive at a deal".
When May first disclosed her plans to opt into 35 EU justice measures including the arrest warrant in 2012, they met little outcry in parliament. The recommendations coincided with her announcement that she had dropped a bid to extradite computer hacker Gary McKinnon to the United States, which delighted many in her party who regarded the UK-U.S. extradition as imbalanced.
But the issue blew up two years later when she sought to force the measures through parliament. May initially misjudged the level of protest but successfully faced down the rebels, and later said: "I wasn't trying smoke and mirrors."
But for many Conservatives and members of opposition parties, her behaviour left a bad taste.
"It's not so much about how do you steel yourself, it's about, 'Are you doing the right thing?'" May told the Sunday Times late last year.
"If you know you are doing the right thing, you have the confidence, the energy to go and deliver that right message." (Reporting by Elizabeth Piper; Editing by Pravin Char)