Variable speeds

This one was from Saturday that I forgot to mention. Heading back from Kidderminster through the main streets I ended up behind a car travelling just below the speed limit of 30mph - fair enough. Up to the Railway bridge and we entered a 40mph - still travelling at around 30mph - okay maybe he missed the sign. Approaching the first set of stupidly placed traffic lights and into a national speed limit (60mph) still 30ish over and approaching the next set of lights on green and I'm about to indicate and overtake when the car behind me just pulls out and speeds past; I indicate and follow.

We both overtake several cars and hit the end together and slow down back to 30mph. Through into Gilgal and I indicate and switch lanes, the car in front just switches lanes. Through into Mitton Street and I indicate and switch lanes the car in front just switches. Then I hear a car roar and this little car speeds past the pair of us, indicates and pulls over into the other lane, then speeds down Lion Hill and indicates and pulls into the moving queue of traffic.

Yep it's the same car that we had been following before - R202 MAB. Perhaps they could explain why when travelling on low-traffic, straightish, wide rides you should travel at 30mph, but on bending, narrow, high-traffic ones speed is the best policy?