Interesting! I've just been out and checked mine (07 Ed30) and there is a bit of play. It's not solidly located like the clutch and throttle pedals, but it's only about a mm I'd say. I don't feel any movement in the pedal at all under normal braking.
If you're braking over bumps, are you sure it's not just the ABS kicking in? It's pretty sensitive in these cars I've found. I get that with my winter tyres if I brake a little hard, just pulses the pedal very briefly, which could feel like a bit of play I guess?