Speaking in Tokyo, at a UK embassy event promoting startups, he said: "Once the toothpaste is out of the tube, that's it. We have to strike a balance."
"We licensed Uber a while ago in the knowledge that it will prove very difficult for the established black cab trade. We have to make sure that we do what we can to give the black cab trade a level playing field," Bloomberg reported.
Uber faces curbs in London to several features, subject to a 12-week consultation period and a final decision by Transport for London in the new year. These include introducing a waiting time of five minutes, banning shared rides with other people as well as displaying nearby drivers’ availability on apps.
In his weekly column for the Telegraph, Johnson has said he thinks Uber drivers' ability to ply for hire is illegal under minicab laws, a position long-argued by London's black cab drivers. However, he added that the proposals are not about blocking the app, but enabling it to exist alongside the black cab trade.