Home Secretary Amber Rudd has maintained that the UK wants to keep a "deep and special partnership" with the EU after Britain finalises its departure from the bloc.
It follows comments from German Chancellor Angela Merkel which suggested her country should no longer rely on Britain and the US after Brexit and the election of President Donald Trump.
Merkel said Europeans needs to "take our fate into our own hands," but Rudd insisted that need not be the case.
"As we begin the negotiations about leaving the EU, we will be able to reassure Germany and other European countries that we are going to be a strong partner to them in defence and security, and, we hope, in trade," Rudd told the BBC Radio 4's Today programme on Monday (29 May).
"This is going to be the most important negotiation that this country has embarked on for many decades. Making sure that we get this right is going to be absolutely critical, and we don't underestimate the difficulty.
"We can reassure Mrs Merkel that we want to have a deep and special partnership so that we can continue to maintain European-wide security to keep us all safe from the terrorists abroad and those that are trying to be nurtured in our country."
Merkel's comments came at a campaign event in Munich after returning from the G7 summit with other world leaders in Taormina, Sicily.
She and others were trying to convince Trump of the benefits of the Paris climate agreement to Trump, but he walked away from the summit without making any firm commitments on the deal.
Merkel, who has a doctorate in quantum chemistry, was clearly frustrated by the US president's non-committal and told Germans at the rally: "The times in which we could completely depend on others are on the way out.
"I've experienced that in the last few days. We Europeans truly have to take our fate into our own hands."