Defence Secretary Sir Michael Fallon has stepped up calls to NATO allies to boost their military spending to counter the growing threats of terrorism and cyber warfare.
Attending a meeting of alliance defence ministers, Sir Michael echoed demands by US President Donald Trump for all member states to meet the NATO target of spending 2% of GDP on defence.
The two-day gathering in Brussels marked the first visit to NATO headquarters of new US Defence Secretary General James Mattis since taking office last month.
During the election campaign, Mr Trump rattled some members by describing the alliance as "obsolete" and questioning US commitment to the defence of Europe.
Since becoming President, however, he declared his support for Nato while insisting other member states must bear more of the burden of the collective defence.
Ahead of the talks, NATO Secretary General Jens Stoltenberg was keen to highlight figures showing the European members and Canada had raised their defence spending by 3.8% in real terms last year.
However, NATO officials confirmed that the UK - along with the US - remained one of just five member states to meet the 2% target.
On Tuesday, the Ministry of Defence flatly rejected a claim by the International Institute for Strategic Studies think tank that the UK spend had actually dipped below 2%.
Sir Michael - who had a one-to-one session with General Mattis - re-iterated Britain's support for demands for the other member states to do more.
"NATO has been a guarantee of mutual security for more than half a century," he is expected to say.
"Britain is now calling for our partners to step up and share burdens on spending and help it become more agile in dealing with new threats including cyber and terrorism.
"As leading player in the alliance we recognise the importance of backing up our operational and exercise commitments with investment in new equipment to deal with threats to our security."