Richard Barnes, who was deputy mayor from 2008 to 2012, said that the three main parties did not “speak the language of normal people”.
The defection appeared to be deliberately timed, coming just hours before Mr Johnson’s speech to conference on Tuesday morning. However, it later transpired that Mr Barnes was deselected from the party more than a year ago and stood as an independent candidate for Hillingdon council in May.
Mr Barnes was London Assembly member for Ealing and Hillingdon from 2000 to 2012, and is a former Hillingdon councillor. He may stand for elected office for Ukip but not for the House of Commons.
He followed Douglas Carswell, a maverick eurosceptic, who unnerved the Tory high command by joining Ukip in August.
Nigel Farage’s party is now based in offices in Mayfair – lent by a wealthy supporter, Andrew Reid – which were previously used for Mr Johnson’s re-election campaign.
The mood at the conference in Birmingham has hardened against the defectors, with Liam Fox, former defence secretary, describing the behaviour of Mr Reckless as “loathsome”.
Mr Johnson joked on Monday night that the defectors were the sort of people who might inflict “barely credible” injuries on themselves by “vacuum cleaner abuse”.
Some MPs, however, are furious with Mr Reckless and the timing of his decision to quit the party.
Mr Barnes said he wanted the UK to pull out of the EU and revert to a trading agreement with continental Europe, accusing David Cameron of making “unrealistic” attempts to renegotiate the country’s relationship with the bloc.
“There seems to be a detachment from ordinary people’s lives in the Westminster village,” he said. “The parties just don’t seem to relate and talk the language of normal people.”
He also accused the coalition of failing to tackle immigration, warning that Britain’s borders were “massively porous”.
“At the moment it’s a mess. We don’t count people in, or count them out. That would be a good place to start,” he said.
Mr Barnes, who is gay, dismissed claims Ukip was homophobic. “I’ll stand my ground against any prat. They are in all the parties. I don’t think they become homophobic the moment they join Ukip,” he said.