Britain said Saturday it was sending more troops to Iraq to bolster its mission training up the armed forces taking on the Islamic State jihadist group.

Defense Secretary Michael Fallon said a further 30 troops would be deployed to provide training in logistics and bridge-building, as well as specialist medical staff.

Prime Minister David Cameron stands accused of unleashing "Project Fear" to try and keep Britain in the EU at a June referendum -- but experts say both camps are resorting to negative campaign tactics to win support.

Cameron's old friend and nemesis Boris Johnson, who came out for Brexit in a surprise snub to the premier last month, has led the attacks with a string of well-crafted broadsides accusing the "Remain" camp of scaremongering.

Mayor of London Boris Johnson on Saturday came out fighting for Britain to leave the European Union, warning that the country had "given away control of our destiny".

The charismatic politician electrified the campaign for the June 23 referendum by declaring last weekend that he backed a so-called Brexit, positioning himself against Prime Minister David Cameron.

EU president Donald Tusk insisted on Wednesday that the bloc's top court cannot overrule Britain's renegotiation deal, weighing into a debate between Prime Minister David Cameron and a top minister.

British Justice Secretary Michael Gove -- who backs a British exit from the European Union -- said earlier in the day that the agreement by Cameron and European leaders at a Brussels summit last week was not legally binding.

Prime Minister David Cameron on Monday warned that Britain's departure from the European Union would threaten its economic and national security, as the pound plunged on Brexit concerns.

"Leaving Europe would threaten our economic and our national security," Cameron said in a report to parliament after dozens of MPs from his own Conservative party said they will vote for Brexit, including London mayor Boris Johnson.

The rival campaigns for Britain to leave the European Union or stay part of the 28-member bloc are taking shape ahead of the June 23 referendum.

Here are the key players in the debate:

London mayor Boris Johnson on Sunday said he would support a vote for Britain to leave the European Union in a blow for Prime Minister David Cameron ahead of a membership referendum in June.

"After a great deal of heartache... I will be advocating vote Leave," said Johnson, a popular politician from Cameron's own Conservative Party who is seen as a potential successor to the prime minister.

French President Francois Hollande said Thursday an EU deal with Britain was "possible" but ruled out any terms that would hold the bloc back, amid concerns over demands for safeguards for non-euro countries.

"A deal is possible if certain conditions are met. A deal is possible because it is necessary that Britain should remain in the EU," Hollande said as he arrived at a Brussels summit.

European Commission chief Jean-Claude Juncker said Tuesday he could not imagine Britain leaving the EU as Prime Minister David Cameron drummed up support in the European Parliament for his reform proposals.

Cameron came to Brussels for talks with Juncker, European Parliament head Martin Schulz and top MEPs aiming to win them over to the changes he says Britain must get to avoid “Brexit”.

English town halls and publicly funded universities face "severe penalties" if they institute boycotts of "unethical" companies or Israeli goods under controversial new rules to be outlined by the government this week.

"Locally imposed boycotts can roll back integration as well as hinder Britain's export trade and harm international relationship," the Cabinet Office said in a statement on Monday.