Storm Shadow missiles supplied to Ukraine by Britain have been used in Russia, according to reports.
Wreckage from one of the long-range weapons has been found in Russia’s Kursk region, which borders Ukraine, several media outlets have said.
Storm Shadow’s use in Russia comes a day after Moscow said American long-range weapons had been fired into its territory.
Russian President Vladimir Putin has lowered the threshold for using nuclear weapons, after US President Joe Biden gave Kyiv permission to fire US ATACMS long-range missiles into Russia.
Downing Street would not comment on the reports.
Number 10 has previously refused to comment on any changes in policy about allowing Kyiv to use long-range missiles in Russia.
In the House of Commons, shadow defence secretary James Cartlidge raised a point of order, asking whether ministers were expected to make a statement on the reports.
Defence Secretary John Healey had earlier told MPs he had spoken with his counterpart in Kyiv on Tuesday where they discussed the UK’s plan to support Ukraine.
Mr Healey told the Commons on Wednesday: “We’ve seen over recent weeks significant change in the action and in the rhetoric on Ukraine, and Ukraine’s action on the battlefield speaks for itself.
“We as a nation and as a Government are doubling down on our support for Ukraine and determined to do more. I discussed this with (Ukrainian) minister (Rustem) Umerov in a call yesterday where he talked about the robust response that Ukraine is making to recent Russian escalations.”
Earlier on Wednesday, the US closed its embassy in Kyiv because of a “potential significant air attack” by Mr Putin’s forces.
Britain’s mission to Ukraine remains open, but the Foreign Office said the safety of staff and British nationals is of “paramount” importance and the posture and travel advice will be kept under review.
The embassy in Kyiv has been operating a limited diplomatic function in recent months and not providing in-person consular assistance.
