Theresa May has warned Donald Trump not to ignore the “malign behaviour” of Russia when he meets President Vladimir Putin in Helsinki.

Downing Street insisted the Prime Minister welcomed Mr Trump’s decision to “engage” with the Russian leader in the Finnish capital on Monday.

However No 10 also made clear that she expected him to raise issues like the Salisbury nerve agent attack on former spy Sergei Skripal and his daughter, Yulia.

Visit by President TrumpTheresa May will press Donald Trump on Russian relations (Stefan Rousseau/PA)

Officials said she made her position clear at the working dinner on Wednesday at the Nato summit in Brussels.

Following the summit Mr Trump complained again that alliance members were not spending “nearly enough” on defence.

The president tweeted: “Europe’s borders are BAD! Pipeline dollars to Russia are not acceptable!”

In remarks released by Mrs May’s office, she said that when it came to dealing with Russia, it was essential to do so from a position of strength underpinned by alliance unity.

“As we engage Russia we must do so from a position of unity and strength, holding out hope for a better future, but also clear and unwavering on where Russia needs to change its behaviour for this to become a reality,” she said.

“And, as long as Russia persists in its efforts to undermine our interests and values, we must continue to deter and counter them.”

Visit by President TrumpSecurity preparations ahead of Donald Trump’s visit to the UK (David Mirzoeff/PA)

Mr Trump’s decision to meet Mr Putin was widely seen as a blow to her attempts to isolate Russia following the Salisbury incident in March.

Her comments now are likely to be seen as an attempt to to deal with a difficult issue ahead of Mr Trump’s first visit to the UK as president starting Thursday.

Stressing the importance of Western unity, she said it was essential for allies to work together “to raise the cost of malign behaviour whenever it occurs”.

She highlighted the attack on the Skripals as an example of “a well-established pattern of Russian behaviour to undermine our democracies and damage our interests around the world”.

“In recent years we’ve seen Russia stepping up its arms sales to Iran; shielding the Syrian regime’s appalling use of chemical weapons; launching cyber-attacks that have caused huge economic damage; and spreading malicious and fake news stories on an industrial scale,” she said.

She added: “Our long term objective remains a constructive relationship with Moscow.

“If we are to be successful in this we must keep engaging individually and as an alliance.

“That is why I welcome President Trump’s forthcoming meeting with President Putin, open channels of communication between the US and Russia are key to managing the risks of confrontation.”