British fighter jets shot down "a number of drones" fired at Israel from Iran, Prime Minister Rishi Sunak said.
The UK was one of several countries, including the US, which helped counter Iran's unprecedented attack - its first ever direct strike on Israeli soil.
Additional RAF jets were deployed over Iraq and Syria, not Israel, the Ministry of Defence (MoD) said.
Mr Sunak, who condemned Iran's "reckless attack", will join G7 leaders on Sunday to discuss next steps.
Speaking to journalists in Downing Street, Mr Sunak said if Iran's attack on Israel been successful "the fallout for regional stability would be hard to overstate".
He did not specify how many drones were shot down by British forces.
Attack drones were intercepted by the RAF in Syrian and Iraqi airspace, where it was already operating as part of the Operation Shader mission against the Islamic State group.
The MoD did not say how many RAF Typhoons were airborne but said the RAF would repel "any airborne attacks within range" of its operations in the region.
Iran launched hundreds of aerial drones and cruise missiles at Israel overnight on Saturday and into Sunday, in a widely anticipated retaliatory attack.
The Israeli military said it had intercepted the majority of the attacks - mostly outside of Israel's airspace - with the help of other countries.
The US was one of those allies, with President Biden confirming the US military helped Israel shoot down "nearly all" of Iran's drones and missiles.
Jordan also assisted in taking out some Iranian drones, according to security sources cited by the Reuters news agency.
Mr Sunak said it was clear Iran was "determined to sow discontent and destabilise the region, its own backyard".
He went on to pledge the UK's continued support for the security of Israel and the wider region and called for "calm heads to prevail".
"We'll be working with our allies to de-escalate the situation and I look forward to speaking to G7 leaders this afternoon," he said.
Iran's attacks come after Tehran vowed to retaliate over a strike on its consulate in Syria on 1 April, which killed seven Islamic Revolutionary Guard Corps officers, including a top commander.
The Iranian government has accused Israel of carrying out that attack, but Israel has neither confirmed nor denied it.
Labour leader Sir Keir Starmer said the party supported all measures "designed to restore calm" and prevent a wider regional war.
In a statement, he condemned Iran's "decision to subject Israelis to these unacceptable attacks".
"The international community has been united in urging restraint and we regret that yet again Iran has chosen a different, dangerous path," Mr Starmer added.
Shadow home secretary Yvette Cooper told the OceanNewsUK that Labour wanted to hear from the prime minister in Parliament on Monday because of the "seriousness" and "real concerns about potential escalation".
Conservative MP Tobias Ellwood, who chaired the Commons Defence Select Committee until his resignation over comments made about Taliban-rule in Afghanistan, told OceanNewsUK: "When it comes to a state-on-state attack, it's very clear that Britain will stand with Israel to defend its skies and soil."
But he said allies would be encouraging Israel "to take stock, to think carefully before responding otherwise this could tie the Middle East up into a wider regional war that would invariably include Israel's ally the United States".
