The plans have been heavily criticised by parks campaigners, but Johnson said he had no intention of exploiting the sites: "We don't want to commercialise the Royal Parks in any way. We want to work sensitively with local people so that we can make the best of them."
The Department for Culture, Media & Sport (DCMS) issued a statement saying measures would be taken to ensure the parks' identities would not be affected by the change and that clear links would be established between the new management and other London-wide issues such as transport, tourism and the environment.
The Royal Parks Agency, which runs the sites, is facing around 30 per cent budget cuts by 2013 from its annual DCMS grant.
Johnson said he would try to encourage US-style philanthropy to make up the shortfall. "I'm interested in what's happening in New York, where groups of extremely affluent members of the community put a serious amount of money into their parks. We want to try to stimulate that here," he explained.
But he warned that he would not accept responsibility for the parks if the Government withdrew all funding. "We aren't taking on these parks as some kind of crazed budget dumping exercise," he insisted. "The dowry has got to come."