The former cabinet minister Priti Patel has called for the election watchdog to investigate spending by the remain campaign in the EU referendum.

The Brexit-backing Tory MP questioned the impartiality of the Electoral Commission and said it should either investigate Britain Stronger in Europe or end its inquiry into the Vote Leave campaign.

Her complaint follows claims relating to a video featuring the actor Keira Knightley urging people to vote. The video was published on the Britain Stronger in Europe website and Facebook page in the final days before the vote in 2016, the Sunday Telegraph reported.

Britain Stronger in Europe said Patel’s complaint showed a “complete lack of understanding of electoral law” and noted that a previous complaint of Patel’s had been dismissed.

The clip featuring Knightley was produced by an advertising agency, along with a series also featuring the designer Dame Vivienne Westwood and the model Lily Cole, at a total cost of more than £76,000.

The Don’t F*** My Future videos were reported to have been commissioned by other campaign groups but Patel said she had “deep concerns” about collusion between remain-supporting organisations that may have allowed the official Britain Stronger in Europe campaign to breach the strict £7m spending limit.

This month the Electoral Commission fined the campaign body Leave.EU £70,000 and referred its chief executive, Liz Bilney, to the police after it found it had breached multiple counts of electoral law during the referendum. The commission also found that Leave.EU inaccurately reported three loans it had received from companies controlled by its co-founder Arron Banks, who described the fine as “a politically motivated attack on Brexit”.

In a letter to the Electoral Commission, Patel said: “I am sure you share my deep concerns that Britain Stronger in Europe seems to have been provided with services by other remain campaigns without declaring the expenditure in the appropriate way.

“There is evidence that many campaigns appear to have acted as a mere continuity of the official remain campaign as it approached its spending limit, the most egregious example of this being the regrettably named ‘Don’t F*** My Future’ campaign, which many different remain organisations appear to have involved themselves in.”

A previous call for an investigation by Patel was rejected by the Electoral Commission, but the leading Vote Leave figure said that “serious questions about the impartiality” of the watchdog had been raised.

She said the newly reported material coupled with the evidence made public this year “suggests that the commission has decided to hold leave campaigns to one standard, and remain campaigners to another, much lower standard”.

In her letter to the watchdog’s head of regulation, Louise Edwards, Patel said: “I believe that the Electoral Commission has an important role to play in our democracy, but that role comes with an important responsibility: to be politically neutral at all times.

“If you want to restore confidence in the commission, you should either start a formal investigation into Britain Stronger in Europe, or show equity and end the investigation in Vote Leave.”

A spokesman for Britain Stronger in Europe said: “Following hot on the heels of the dismissal of her previous complaint in December 2017, this demonstrates Priti Patel’s complete lack of understanding of electoral law. It is common practice for campaigns to post third party content on social media.”

The campaign said it was confident the complaint “would be dismissed as quickly and comprehensively as her other politically motivated and unsubstantiated claims have been”.

“Britain Stronger in Europe always took our legal responsibilities seriously and have always followed the rules around working together, which has been backed up by the Electoral Commission,” the spokesman said.

An Electoral Commission spokeswoman said: “We have not received the allegation formally yet but when we do we will consider it in line with our enforcement policy.”