Prime Minister Boris Johnson said:
"The loss of life on Ukrainian International Airlines Flight 752 is a tragedy and my thoughts are with all of those who lost loved ones.
"Four British nationals were among those who were killed, and we are providing support to their families at this most terrible time.
"There is now a body of information that the flight was shot down by an Iranian Surface to Air Missile. This may well have been unintentional.
"We are working closely with Canada and our international partners and there now needs to be a full, transparent investigation.
"It is vital that there should be an immediate and respectful repatriation of those who’ve lost their lives to allow their families to grieve properly.