The Press Association news agency said Cameron told journalists at a press lunch about the time Health Minister Simon Burns backed into Speaker John Bercow's car. When Bercow said he was not happy, Cameron said Burns retorted: "So which one are you?" Bercow stands about 5 foot 6 (1.68 meters).

The Walking with Giants Foundation charity, which helps people with restricted growth, said Cameron's gibe was "downright appalling."

Its co-founder John Connerty, said Thursday that Cameron's remarks were "totally unacceptable." Cameron's office said his "lighthearted comments" were not meant to offend.