Boris Johnson to campaign for Britain to leave Europe

Boris Johnson is expected to announce tonight which side of the "Brexit" debate he supports.

It is widely expected the London mayor will come down on the side of Britain leaving the European Union when he reveals his decision in his Daily Telegraph column, which will be tweeted at 10pm.

Today his sister insisted Mr Johnson was not "milking" the announcement for "maximum publicity."

Writer and broadcaster Rachel Johnson said her brother had to make a "very, very hard choice."

"This is an enormously complicated decision for everybody, not just Boris... and his participation in either camp is going to be very significant, and this is why he's taking so long to decide," she told Sky News.

Boris Johnson said he is to campaign for Britain to leave the European Union in the forthcoming in/out referendum.

Boris Johnson to end speculation about his Brexit position in 25 minutes.

London's mayor will make a statement outside his Islington home at 5pm, writes Simon Harris.

Conservative mayoral candidate Zac Goldsmith will vote for Britain to exit the EU, his mayoral campaign have confirmed.

It is understood that Boris Johnson will tweet his decision via his Daily Telegraph column at 10pm

Labour Mayoral candidate Sadiq Khan has said that Britain remaining in the EU is "vital" for London's growth.

Mayoral candidate Caroline Pidgeon has said it would be "insane" to leave the EU, responding to news that Britain will vote on a referendum on June 23.

The Liberal Democrat candidate said she will make the case for Britain to stay in the EU.

• David Cameron announces June referendum