By Kylie MacLellan and William James

LONDON (Reuters) - Britain must secure control over immigration in divorce negotiations with the European Union, Stephen Crabb, the first candidate to put himself forward to succeed David Cameron as British prime minister, said on Wednesday.

Work and pensions minister Crabb, who supported Britain staying in the EU at last week's vote, ruled out holding another referendum and said his Conservative Party and the country must now unite in focusing on negotiating the best Brexit deal.

Cameron, who led the Remain campaign, announced his resignation after Britain voted by 52 to 48 percent to leave the bloc. A leadership contest within the ruling Conservative Party will take place to elect his successor by early September.

Crabb, a lawmaker since 2005, said it was vital Britain sought as close an economic relationship with the EU as it had now but it was also clear immigration curbs would be needed.

"The British people want control of immigration ... For us, this is a red-line," said Crabb, launching his leadership bid alongside business minister Sajid Javid who he said he would appoint as his finance minister if he won the top job.

"Brexit needs to do what it says on the tin," he said, adding that Britain should begin discussions about a free-trade deal with the EU immediately and would demand the supremacy of UK law over EU law.

He said it would be challenging to reconcile control over immigration with full access to the single market but the task of a future government "must be to get a set of arrangements that approximates as closely as possibly what we have now."

The Brexit vote has triggered one of Britain's biggest crises in modern times with both major political parties in turmoil, more than $3 trillion wiped off global stocks and one of the steepest falls in sterling in a generation.

Crabb dismissed the prospect of holding a snap election if he becomes prime minister, saying: "The answer to the question of instability is not to create further uncertainty".

Urging his party to unite, Crabb said the leadership contest, which former London mayor Boris Johnson and interior minister Theresa May are also expected to join before Thursday's nomination deadline, should not be defined by labels like "Remain" or "Leave".


Speaking in a packed room against a blue backdrop emblazoned with the slogan "A plan for unity and opportunity", Crabb emphasized his working-class roots, which has led him to be dubbed the "blue collar ticket" by some newspapers.

It contrasts dramatically with that of bookmakers favorite and leading "Out" campaigner Johnson, who like Cameron attended elite private boarding school Eton and Oxford University.

"I worked every week from the age of twelve, starting at the local corner shop, graduating to the Tesco shop floor. I paid my way through university working on building sites in different parts of the country," said Crabb, who was born in Scotland and brought up in public housing in Wales by his single mother.

Crabb's background compares with that of Conservative icon Margaret Thatcher, the longest-serving British prime minister of the 20th century who had a modest upbringing as the daughter of a grocer.

The frontrunner has rarely succeeded in winning Conservative leadership battles in the past, and Thatcher surprised the political establishment in 1975 by winning control of the party after starting the contest as an outsider.

A poll by grassroots Conservative website Conservative Home published on Wednesday put May narrowly ahead of Johnson on 29 and 28 percent respectively, with Crabb on 9 percent.

"I know what the odds are and I am not afraid of being the underdog," said Crabb, 43.

"The blend of qualities I bring are exactly those that are needed if we are to get through the difficult circumstances we are in: Resilience, optimism, humility, strength."

(Additonal reporting by Estelle Shirbon; Editing by Guy Faulconbridge and Toby Chopra)