Earlier this year Lord Cameron, the former foreign secretary, met president Zelensky in Kyiv, where he made comments about Ukraine’s right to defend itself which were interpreted by Russia as a “dangerous” threat to use British gifted missiles on Russian territory.

Admiral Sir Tony Radakin, the Chief of the Defence Staff, later clarified that the cruise missile could only be used inside Crimea and the mainland of Ukraine.

Jamie Shea, a former Nato official, on Wednesday responded to Sir Keir’s statements on the Storm Shadow as giving Mr Zelensky a “shot in the arm”.

The Ukrainians “have to be able to strike back against those significant military targets,” he said.

But on Thursday, Mr Zelensky appeared to recognise that full permission for cross-border strikes had not been granted.

“We have got very good messages from the UK leader” he told a Nato press conference, but said no decision had been made yet.

Britain’s strategic defence review will be launched next week, setting out how Sir Keir intends to meet his spending target.

Announcing the review, John Healey, the defence secretary, insisted that seeking closer defence ties with Brussels would not bind the UK into a European defence force.

The Defence Secretary said, however, that Britain would seek to join more EU military programmes.

He suggested that Britain could seek to join more areas of the EU’s permanent structured co-operation (Pesco) programme.

The UK is already part of one Pesco scheme on moving military equipment across the EU.

Mr Healey said: “So we’ve proved we can do it. There are one or two other programmes which may well be programmes in which we have a unique contribution to make and we can get a great deal out of being part of a programme like that.

“That does not require any new formal agreement, it does not require a EU-UK security pact in order to do that.”

Mr Healey acknowledged that talks on the formal UK-EU security pact sought by the Government were unlikely to start this year.

“In a way the declaration in week one from the new Government is seen as significant by the European Union and its members,” he said.

“You’ll know that the European Union, European Commission takes a good few months to get itself sorted out and so it won’t be until the end of the year that it’s really in a position to start doing any sort of detailed discussion with us.”

However, Ben Wallace, the former defence secretary, told The Telegraph: “It is not a new assertion that the UK supports international law of a state defending itself from an aggressor. Part of that law has been the ability for the defender to use weapons to target military facilities engaged in aggression in another state, in this case Russia.

It’s just a restatement of the Government’s permission.”