Police are in danger of encouraging "predatory men" to rape women by discrediting victims in their investigations, the former senior Metropolitan police officer Brian Paddick has claimed.

In a Guardian interview, Paddick warns that some detectives adopt a "she wants it really" attitude to women alleging rape and sometimes refuse to acknowledge that some types of men, such as licensed cab drivers, can be rapists.

The former deputy assistant commissioner is placing the Met's mixed performance on dealing with rape at the heart of his campaign as the Liberal Democrat candidate in May's London mayoral election. Paddick, who told the Leveson inquiry this week that he toned down a Met report about its handling of rape on the instructions of senior officers, is launching a poster and online campaign highlighting the Met's poor record.

Paddick tells the Guardian: "When you look at the very low conviction rate; when you read the testimony of rape victims who say that, whilst the initial police response was good, when the detectives got involved they seemed to be determined to undermine the allegation – then predatory men are going to take some encouragement from that. If predatory men believe that the police will try and discredit the victim, then that could encourage them to commit offences of rape."

The former Met officer warns that police often make the assumption that women are partially or totally responsible if they have been flirtatious. "This is not confined to the police service, this is an attitude in society generally," says Paddick. "I can remember a senior officer saying to me: 'Oh yes, this woman went round and started playing strip poker with this guy.' She subsequently claimed that she'd been raped and he said: 'Well, she'd been asking for it.'

"You know this idea that when a woman says no, she doesn't actually mean no, she's not actually saying no, she wants it really, is something we have to address as an attitude in society as well as an attitude in the police. Unfortunately, the two things reinforce themselves in the police."

The campaign by Paddick, 53, who came third in the 2008 mayoral contest behind Boris Johnson and Ken Livingstone, shows that he sees his 30-year career as a former police officer as central to his appeal to voters. In his Guardian interview, he says:

• The riots of last August will be repeated if the police do not improve relations with Britain's black communities. "We had riots in August which if the police do not transform themselves we will have again," he says.

• The Lib Dems have become the "whipping boys" for the coalition and he will be campaigning to the left of Nick Clegg. "It's quite obvious where I'm positioning myself and it's to the left of the coalition. What we are saying to Londoners, is this has got nothing to do with national politics. We are putting forward an innovative, radical Liberal Democrat agenda for Londoners and that's what we want them to vote on."

Paddick is making rape the centrepiece of his campaign because some of the problems about rape cases that Paddick identified in his original report for the Met have not been addressed. The report found an 18% increase in the number of allegations of rape, but a fall in the percentage of allegations classified by police as rape during 2001-05. He cites the joint report this week by Her Majesty's Inspectorate of Constabulary and the Crown Prosecution Service, which found that nearly 12% of all recorded rape cases in England and Wales in 2010-11 were officially logged as "no crimes". The report said a rape case should only be "no-crimed" if the victim states that it did not happen.

Paddick says: "The police have been placing far too much emphasis on performance rather than on a victim-centred approach to rape. We know that rape is a very difficult offence to secure a conviction on and the easiest way to improve your performance in terms of clear-up rate is not to solve more rape cases, it's to write off more allegations as not having taken place, or some other reason why the thing should not be recorded as a crime. It's much easier to improve your performance that way than it is by putting more effort and time into securing convictions."

Paddick says police also need to widen their horizons when they are considering likely rape suspects, citing the case of John Worboys, the licensed taxi driver jailed indefinitely in 2009 for drugging and sexually assaulting 12 women.

A 19-year-old victim told the Guardian in 2010 that police laughed at her and told her she had been drunk after she alleged that Worboys had raped her. A report by the Independent Police Complaints Commission in 2010 highlighted "individual and systemic" problems within the Met investigation.

Paddick says: "That's a specific example of the police attributing to a category of citizen – black-cab drivers – an assumption of innocence if you like. The Worboys case proves it is not justified and it is a clear warning sign to the police that they need to take all allegations of rape very seriously, no matter how incredible they might think the allegation is."