Rishi Sunak will argue that Britain is safer under the Conservatives against the backdrop of two escalating conflicts likely to dominate the week.
In the last few days, the prime minister has broken with US President Joe Biden by insisting the UK should continue to supply arms to Israel.
It comes as Israeli PM Benjamin Netanyahu appears poised to mount another massive military operation in the southern Gaza town of Rafah against warnings from the US and UK.
Meanwhile, there are fears in Whitehall that Russia could mount an operation on Kharkiv by the end of the week to retake Ukraine‘s second-largest city.
Both operations could trigger wider repercussions.
Amid this worsening global outlook, the Conservatives want to highlight what they say is the gap between Tory and Labour pledges on military spending.
After the initial announcement, Sunak wants to ensure he gets full public credit for the big spending commitment while pushing Labour on its failure to match the promise.
Labour says that the Tory spending plan does not add up.
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Israel arms embargo ‘not a wise path’
On Monday, Sunak will use a set-piece speech to mount the argument that there is a need for security at home and abroad in an ever-increasingly dangerous world and describe the country as being at a crossroads at the next general election.
In a further major political dividing line, Labour has broken with the government and called this weekend for a suspension of arms to Israel, placing it alongside the United States.
However the Tory government is holding firm, arguing that now is not the time and that Britain only supplies a small amount of the munitions used by Israel.
Some people inside government suggest that the US government position is driven by President Biden’s need to take a tougher position to shore up votes in the upcoming election race.
Sunak’s Monday speech is one part of a set of security-themed announcements by the government, following Lord Cameron’s media blitz at the weekend.
On Monday, deputy foreign secretary Andrew Mitchell will address a Tory-leaning think tank, while on Tuesday Defence Secretary Grant Shapps will make a speech, with Chancellor Jeremy Hunt speaking on Friday.
Also, Deputy Prime Minister Oliver Dowden will lead a trade delegation this week to Saudi Arabia.
Although boosting trade will be the focus, Saudi Arabia, like Qatar, is one of the backchannels used by the UK to deliver messages to Hamas.