The assets of the five — who include two people who have been formally charged by US authorities over the case — were frozen under Britain’s Terrorist Asset-Freezing Act, it said in a statement.
Those affected include Manssor Arbabsiar, 56, an Iranian used-car salesman who is a naturalised US citizen living in Texas and was arrested in the United States last week over the plot, the statement said.
Another is high-ranking Revolutionary Guard official Gholam Shakuri, 47, who is the other person charged over the plot but who is believed to be in Iran, it said.
The others are Qasem Soleimani, Hamed Abdollahi and Abdul Reza Shahlai, who US officials said were senior officers in Iran’s Quds Force involved in the plot.
Soleimani is already listed by the European Union as being involved in providing equipment to help the Syrian regime suppress protests.
US authorities last week froze the assets of the same five individuals.
The US Treasury Department has also hit Iranian airline Mahan Air with sanctions, saying it secretly transported members of a military force accused of involvement in the plot.
Authorities in the United States say the plot involved Arbabsiar allegedly trying to contract a Mexican drug cartel to kill the Saudi ambassador, Adel al-Jubeir, possibly through the bombing of a Washington restaurant.
Iran has repeatedly denied any involvement and claimed the allegations are politically motivated.
