Have you seen the red bikes around London? They are called “boris bikes” due to the previous Mayor of London but actually belong to Santander… I love them, it’s so much faster than other transports in the city, you get to visit new neighbourhood and do some exercise! at £2 per day with every 30min free (if you cycle along the river for example every 25min put the bike back, walk to the next station and hop back on again!) or £90 for the entire year (still cheaper than 1 month of Oyster…). You can pay directly at the bike station using a credit card, or have your own Santender key once you apply for the year!
But please beware of buses and taxis! Wear a Helmet, stay focussed and look your itinery first, there is plenty of brand new cycling path in the city, it might be a detour but it will be safer and faster!