"The door for diplomacy and dialogue remains open. But if Iran chooses not to take that route, then we would seek to hold Iran to account and apply a cost to that", Woodward said in a statement.
The ambassador said the United Kingdom was confident Tehran was behind what it considers to have been a deliberate and tactical attack on the tanker in which one British and one Romanian nationals lost their lives.
"Based on the assessment of the data, the system used in the attack was an Iranian sharp-edge 136 UAV [unmanned aerial vehicle]… manufactured only in Iran", Woodward said.
The Liberian-flagged vessel came under attack on 30 July, when it was sailing northeast of the Omani island of Masirah. Two people – a British national and a Romanian citizen – were killed. Israel immediately put the blame on Iran, a claim the Islamic Republic has vehemently denied.