LONDON, June 5 (Reuters) - Britain's government and local authorities are working closely with the police to guarantee security around the national election, and robust plans have been in place for weeks, Prime Minister Theresa May's spokeswoman said on Monday.

Britain will vote in a national election on Thursday, just days after militants killed seven people and injured nearly 50 in an attack on London Bridge on Saturday night, the third assault in Britain in less than three months.

"There are plans in place for the general election. Police have been working closely with local authorities for several weeks on this. Those plans were developed with the threat level being at 'severe' so they are pretty robust," the spokeswoman told reporters.

"Police review security for all events but we have been working very closely with them and local authorities for some time."

(Reporting by Kylie MacLellan; writing by Kate Holton; Editing by Georgina Prodhan) ((kate.holton@thomsonreuters.com; 0044 207 542 8560; Reuters Messaging: kate.holton.thomsonreuters.com@reuters.net))