Lady Warsi has blamed electoral fraud for the Tories' failure to secure an overall majority at this May's election – and claimed that Labour "absolutely" benefited from the alleged fraud.

The Tory chairman told tomorrow's New Statesman: "[There were] at least three seats where we lost, where we didn't gain the seat, based on electoral fraud. Now, could we have planned for that in the campaign? Absolutely not … "It is predominantly within the Asian community. I have to look back and say we didn't do well in those communities, but was there something over and above that we could have done? Well, actually not, if there is going to be voter fraud."

Asked to reveal which seats she felt the Tories had lost due to alleged fraud, she said: "I think it would be wrong to start identifying them."

She said she had written to Nick Clegg, who is overseeing the coalition government's electoral reforms, to discuss fraud and voter disenfranchisement.

A Labour spokesperson said: "These are unsubstantiated allegations from a Tory party which last year had six activists sent to jail for election fraud. The Labour party takes the strongest possible action against any member convicted of election fraud. If Baroness Warsi has any evidence for her claims she should share it with the authorities."

Warsi also launched an attack on the "anti-Islamic sentiment" of the British press, which she compared to the anti-semitism of the early 20th century.

The minister without portfolio, the first Muslim woman to serve in the British cabinet, told the New Statesman: "If you go back historically – [and] I was looking at some [London] Evening Standard headlines, where there were things written about the British Jewish community less than 100 years ago – they have kind of replaced one with the other."

Warsi referred to the conservative columnist Peter Oborne, who has said that anti-Islamic sentiment is the last socially acceptable form of bigotry in the UK, saying: "That's absolutely true …. If you have a pop at the British Muslim community in the media, then first of all it will sell a few papers; second, it doesn't really matter; and third, it's fair game."

She added that Labour's approach towards ethnic minorities was "so patronising", saying: "The party behaved as if the British Raj was still happening and I was quite appalled at the way BME [black and minority ethnic] communities would respond to that."

She denied she faced discrimination from the Tory party "as an Asian woman", but said: "I think as an Asian, Muslim woman there were blocs, not within the Conservative party, but within the wider Conservative thinking, that had question marks about who I was and what I represented."

Warsi also launched a strong defence of Andy Coulson, David Cameron's director of communications, who has been named in phone-hacking allegations in the Guardian and New York Times. "I have a huge amount of time for Andy," Warsi said of the former News of the World editor. "My judgment of Andy is going to be based on my experience of him. I know that when I went through quite a traumatic divorce, and the media fallout from it when my ex-husband went to the papers, Andy was there for me. I am a deeply loyal person and I honestly believe that you judge people on how you find them. I can only judge Andy on what I have found from him and I have always found him to be a really supportive person."

Warsi also said the Tories were prepared for losses in next May's local elections. "I think we are going to have to temper expectations, purely because, politics aside, from a numbers perspective these elections are the ones that four years ago we did extremely well in. And so 2011 is the year we would expect to lose some seats. It is the first year of government and we will have to make some difficult decisions."

She said that "right now" the plan was for the party to stand in every council seat. "As party chairman, right now, you are asking me this question and my answer is: yes."

Asked about the views of Tory party members about the decision to form a coalition with the Lib Dems, Warsi said she "challenged" the members and told them "we didn't win the last general election … so that means we are compromising all the time".

She added: "First of all, we need to acknowledge how big the deal was that we needed to seal. It was a huge mountain that we needed to climb … and we won more seats at this election than we gained since the 1930s."