i'd recommend either:
2x 30 amp electronizes (£86)
sabertooth 2x25 (£96)
scorpion xxl 2x20 (£100) excluding shipping and tax etc

as your using 18v drill motors instead of 12v i think they'll draw more than 15amps. besides it's only £20 extra for 30amp electronizes than it is for 15amp. better to be sae than sorry