Lomas, who was paralysed in a horse riding accident, lit the cauldron from the English national flame kindled on Scafell Pike, Xinhua reports.
British Prime Minister David Cameron, London Mayor Boris Johnson and London 2012 chairman Seb Coe attended the ceremony.
The relay travels from Stoke Mandeville to London overnight Tuesday for the Games opening ceremony Wednesday.
Cameron said at the ceremony: “After a fortnight of Olympics withdrawal symptoms, it’s time to dust off the GB flags and get ready for two more weeks of spectacular sport.
“Over these next two weeks, we’re going to have more of those moments that will bring us together and make us proud.”