A Labour councillor's home was illegally converted into 'cramped' flats which failed to meet the council's minimum living standards.
Cllr Jiwan Virk became embroiled in the increasingly bitter row over unlawful extensions after being ordered to restore the house in Basildene Road, Hounslow.
Relatives of the Bedfont ward councillor were also told to tear down illegal porches at two neighbouring houses at Monday's meeting of the sustainable development committee.
The revelation comes as a huge embarrassment for his party, which last month highlighted claims by residents that the Tory-led council's crackdown on illegal building work is 'institutionally racist'.
Deputy Conservative leader Mark Bowen called on Cllr Virk to explain why he had failed to declare all three properties on the register of members' interests until last week.
"This is a very poor example to set and he needs to explain himself to the public," he said.
"What's the excuse from the Labour group going to be this time?
"Will they say he wasn't aware of the rules or will they make yet more unedifying allegations against the council?"
Cllr Virk claims the property was already converted into flats when he bought it four years ago, though officers say he has failed to provide sufficient proof.
He also said he had offered to remove the porch and was unaware exisiting properties had to be included in the register of interests every year.
Enforcement officers at Hounslow Council wrote to the occupiers in June 2005, and again in September 2006, following a complaint about a rear extension, but received no response.
It wasn't until they sent a third letter in January last year that Cllr Virk, who claimed he never saw the original letters, finally arranged a site inspection.
A damning report followed, in which officers criticised the 'cramped living conditions' and 'substandard accommodation' experienced by tenants.
"The use harms the living conditions of occupiers of neighbouring properties in terms of a likely increase in vehicle activity, noise and rubbish," it added.
Labour leader Jagdish Sharma said Cllr Virk 'should have known better' and promised that Labour group officers would investigate the matter.