There are around 1,400 UK military and civilian personnel supporting counter-Islamic State operations in Iraq (Picture: US Army).
Britain has raised the threat level for UK forces and diplomats in Iraq because of an increased risk from Iranian-backed militants.
It is also understood British families in Saudi Arabia, Kuwait and Qatar are on an increased state of alert.
There are around 1,400 UK military and civilian personnel supporting counter-Daesh, otherwise known as so-called Islamic State, operations in Iraq.
The UK has trained more than 89,000 Iraqi forces, including more than 13,000 Kurdish Peshmerga, in weapons maintenance, counter IED, medical and engineering skills.
General the Lord Dannatt, former Chief of the General Staff, praised the decision to increase the state of alert.
He said: "The only action that we should be taking is the sort of action that we currently are taking which is to make sure all our personnel and people in that region are aware of the increased risks."
An MOD spokesperson said: "We keep the security of our deployed personnel and assets under constant review.
"There is a range of threats to UK and coalition forces in this part of the world: that is why we have a very robust range of force protection measures.
"The UK has long been clear about our concerns over Iran’s destabilising behaviour in the region."
Foreign Secretary Jeremy Hunt said British officials are worried about the risk of a conflict between the US and Iran which neither side intends.
Mr Hunt told reporters in Brussels: "We are very worried about the risk of a conflict happening by accident, with an escalation that is unintended really on either side but ends with some kind of conflict."
Dr Robert Gutsche, a US politics expert at Lancaster University, said "if Donald Trump is looking for a fight, he might just get one".
Earlier this week, former Royal Navy chief Admiral Lord West said military strikes against Iran would be "an absolute catastrophe", while the NATO Secretary General has expressed his concerns.
The US has already sent an aircraft carrier and four B-52 bombers to the region, and is reported to have tens of thousands of American troops on standby to be deployed to the Middle East.