Use code YOUAREFREENOW to get 50% off your next Free Now minicab, this will work for new and existing customers. Maximum discount £6 so best to use for trips £12 and under Free Now is an Uber alternative available in London operated by BMW and Daimler, myTaxi and Kapten both merged to become Free Now. Only 500 available so it will go quick!
There is also an offer on Amex for 50% back up to £7, should stack with this to potentially give 75% off if you are eligible! Credit to @PropagandaDan for pointing this out.