London's favourite taxi app Hailo are now an official Avios collection partner. Collect 1 Avios per £1 spent on Hailo journeys, excluding airport transfers, by syncing your British Airways Executive Club number to the Hailo app. To celebrate the launch of the partnership, Hailo are offering all new users 400 Avios for their first UK transfer to London airports when you ride before the 31 December 2015. More details on their web site. I'd download the app now and add your BA account if I were you.
It's worth pointing out that Hailo in Spain gives you the 400 avios without even booking a ride - at least that's what happened to me this time last year when I registered. If you're in the UK you should be able to register for the Spanish version of Hailo but it's a bit fiddly. You'll need to use a mobile app called Fake GPS and set your location to Madrid, register for your account (so it sets you up on the Spanish version of Hailo), then log back in as if you're in the UK and enter your mobile number. Then if you log back in as if you're in Spain you should be able to add your Iberia Plus number and get the avios.