The network provider's figures, which were achieved during tests involving around 1,000 people in the London region, are comparable to the top home broadband speeds.
O2 recorded the highest speeds around the Hyde Park, Soho, Westminster, King's Cross, Canary Wharf and South Bank areas. The overall speeds averaged out between 20 and 50Mbps, which is still almost 20 times faster than current 3G technology.
"The forthcoming spectrum auction is a watershed moment for the UK mobile industry, releasing the airwaves that will power a whole range of exciting next generation mobile services," said Ronan Dunne, CEO of O2's parent company Telefonica.
"The new spectrum will increase capacity, quality and speed and will allow us to deliver true connectivity through a suite of innovative digital services that work seamlessly and at speed for the benefit of consumers, business and UK plc."
Everything Everywhere, a joint venture between T-Mobile and Orange's UK operations, also has plans in place to bring 4G coverage to Britain, with recent reports suggesting that it could go live before the end of 2012.
O2 launched its 4G trial in December last year as a precursor to widespread introduction, tentatively scheduled for next year.