It is a known risk that Russia could send captured British anti-tank missiles meant for Ukraine to Iran, the defence secretary has said.
Given that they do not contain cutting-edge technology, however, it would not be a major concern if they fell into Iranian hands, Ben Wallace told Sky News.
At the same time, Britain and other NATO allies were enjoying an "amazing opportunity" to learn about President Vladimir Putin's military capabilities from Russian weapons captured by the Ukrainians, he said.
Mr Wallace said the UK was looking into a Sky News report this week that Moscow had flown British and US anti-tank and anti-aircraft missiles to Tehran along with 140m euros (£122m) in August, which they exchanged for dozens of deadly drones set to be used against Ukraine.
The NLAW, Javelin and Stinger munitions had been intended for the Ukrainian military but had fallen into Russian hands, according to a security source.
"Of course, we don't want to see these things happening," Mr Wallace said. "But fundamentally, that is the risk we took when we decided it was important to help Ukraine."
It also worked both ways, with the UK and other NATO allies able to learn from Russian weapons captured by the Ukrainians.
"Russia has lost significant numbers of its A-grade capabilities - they've been captured in the hundreds and thousands," Mr Wallace said.
"That is an amazing opportunity for NATO countries to understand the technologies that go on in Russian equipment and that will give us a very strategic advantage in the future."
As for the NLAW anti-tank missiles that the UK has given to Ukraine, they are hugely effective pieces of kit, but they are not fitted with next generation technology, which the UK is currently working on, the defence secretary said.
"That will mean there'll be differences in it between what the Iranians - if they do have NLAWs - develop and what we have and that goes the same for the US Javelins… So, I'm not particularly worried. But of course, it was a risk we took as a calculation."
He added: "Iran has a track record of reverse engineering. It's always been very cunning at taking technologies from abroad and trying to turn it into its own capabilities.
"And indeed, the Ukrainian captured Iranian drones that we've seen on the TV that shows a significant number of western components within."