LONDON (Reuters) - New British Prime Minister Theresa May told the first meeting of her senior ministers on Tuesday that they must all play their part in making Britain's exit from the European Union a success.

While May, who backed remaining in the EU ahead of last month's referendum, has appointed Brexit campaigners to several top roles including foreign secretary, less than a third of the ministers in her cabinet backed leaving the bloc.

May told her ministers "it would be down to every person sat around the cabinet table to help ensure that we spread the benefits of leaving the European Union and opportunities ahead to everyone up and down the country," her spokeswoman said.

Footage of the start of the 90-minute meeting broadcast on the BBC showed May sitting next to Foreign Secretary Boris Johnson as she addressed her top team at the long, green cabinet table.

"Brexit does mean Brexit and we are going to make a success of it and we will do that by forging a new role for the United Kingdom in the world," May said.

"But we won't be a government that is defined just by Brexit, we will also be a government defined by the social reform that we undertake," she said, before colleagues banged their hands on the table in a traditional mark of appreciation.

May also told ministers she planned to set up three new cabinet committees -- on industrial strategy, leaving the EU and trade and on social reform -- that she would chair herself to drive the government's top priorities.

Brexit minister David Davis told cabinet colleagues that Britain needed to prepare for the negotiations on leaving the bloc and should consult widely before triggering formal divorce talks with the EU, May's spokeswoman said.

"The prime minister concluded with the fact that Brexit presented a huge opportunity and it was now time to get to it and get on with the job," she added.

(Reporting by Kylie MacLellan and Elizabeth Piper; editing by Giles Elgood)