Mad British taps in baths

A Canadian colleague, now that we are collecting things of strangeness, pondered why British baths need to have two taps with two spouts.  In Canada, he said they would blend to allow the right temperature of water arrive into the bath in a single stream. This seemed very logical and I tried to battle an answer, for example for the convenience of a cold tap to brush one's teeth.  But brushing teeth in the bath is sort of absurd unless you are using the basin to clean your socks or something.  Still, he makes a valid point.