The Latest on Britain's upcoming referendum on whether it should leave the European Union (all times local):

2:15 p.m.

The British head of the European Union's police cooperation agency has warned that the United Kingdom could find it harder to protect its citizens against terrorism and organized crime if it leaves the EU.

Europol Director Rob Wainwright said Monday that if London turns its back on the EU and the police cooperation capabilities it offers, "it would make the U.K.'s job harder, I think, to protect the citizens from terrorism and organized crime."

Speaking at the launch of a new center to fight migrant smuggling, Wainwright said that the British have helped mold cooperation among police forces in the 28-nation bloc, "because it's the unanimous opinion of the British police services that they need that level of engagement."

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12:40 p.m.

The European Union's executive Commission says it will stay out of the referendum campaign on whether Britain should leave the EU.

Commission President Jean-Claude Juncker did campaign last July in a Greek referendum on whether to accept an EU-brokered agreement to secure a massive economic bailout. But chief Commission spokesman Margaritis Schinas said Monday that "we will not take part in this process" ahead of the June 23 poll in Britain.

Schinas did not rule out the possibility that EU commissioner Jonathon Hill, who is from Britain, might campaign in a personal capacity.

Commission officials are appointed, not elected, and often embody the stereotype of the "faceless Eurocrat" that some Britons blame for their country's struggles with the EU.

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09:40 a.m.

British Prime Minister David Cameron is preparing to formally present his plan for a June 23 referendum on Britain's European Union membership to Parliament.

Cameron, who wants Britain to remain part of the 28-nation bloc, will go to Parliament Monday after a weekend that saw London Mayor Boris Johnson announce he is in favor of leaving the union.

The British pound sterling fell in early currency trading Monday on concern that the vote could be closer than expected.

Johnson wrote in The Daily Telegraph that the referendum offers a "once-in-a-lifetime" chance for real change. He says remaining in the bloc would mean more federalism and less democracy.

Johnson is joined by other Conservative Party figures although Cameron enjoys the support of key Cabinet ministers.