Howes was supported by the EPSRC-funded
PPAT project grant number EP/J501360/1 during this work. Hough is supported by the DUEL project financially supported by the Agence Nationale de la Research (grant number ANR-13-FRAL-0001) and the Deutsche Forschungsgemainschaft. Much of the work was carried out under an EPSRC DTA scholarship at Queen Mary University of London. Purver is partly supported by ConCreTe: the project ConCreTe acknowledges the financial support of the Future and Emerging Technologies (FET) programme within the Seventh Framework Programme for Research of the European Commission, under FET grant number 611733
