The Foreign Secretary said the poll had been held against a backdrop of fear that meant the result would not reflect the will of the people.
It was the first chance for voters to go to the ballot box in a major poll since the disputed re-election of president Mahmoud Ahmadinejad in June 2009, which sparked a wave of protests.
Mr Hague said: "It has been clear for some time that these elections would not be free and fair.
"The regime has presented the vote as a test of loyalty, rather than an opportunity for people freely to choose their own representatives.
"The climate of fear, created by the regime's crushing of opposition voices since 2009, persists.
"The field of candidates for this election has been limited by the intensified vetting of candidates, and the ongoing repression of dissent, including the continued house arrest of two of Iran's opposition leaders since February 2011.
"In these circumstances it is not surprising that most of Iran's reformist wing chose not to stand, reducing the elections to an internal competition among regime conservatives.
"As such, we do not believe the elections can be presented as reflecting the will of the people.
"We will continue to urge Iran to address its human rights record, including at this month's UN Human Rights Council."