Brexit Party MEPs abstained from a vote in the European Parliament yesterday to demand Iran release detained dual-nationals, including Nazanin Zaghari-Ratcliffe.
The resolution called on authorities in the country to release EU-Iranian citizens who had been jailed as political prisoners "immediately and unconditionally".
It passed by 608 votes, with seven opposing it, and 46 - including all Brexit Party's MEPs - abstaining.
Belinda de Lucy, the Brexit Party's South East MEP, insisted that although the party felt "very strongly" about releasing detained dual-citizens, voting for an EU foreign policy would be "hypocritical".
"The resolution was not just on the detainees, it was very much about EU foreign policy and the expansion of it, which of course as a party it's very hypocritical to vote for," she told talkRADIO's James Whale.
"We believe the EU foreign policy actually constrains our ability to have independent foreign policy that we might be a bit tougher on. Just go in, swoop her [Zaghari-Ratcliffe] out and put some sanctions on Iran."
She continued: "We just don't think they're [the EU] are tough enough and it's very difficult to put our name to something like that. And of course, we didn't vote against it."
Ms Zaghari-Ratcliffe, a British-Iranian mother, has been held in Iran since her arrest in 2016 for spying – an accusation which she has always denied.
A spokesperson for the Brexit Party told talkRADIO: "It should be obvious that none of us here are bowing to the Iranian regime and that we support the freedom of all who are imprisoned improperly.
"However, we do not usually vote on EU foreign policy issues, as the EU is not a country, and should not even have a foreign policy, in our view."