whiplash claims

Hi everyone, I am in search of some personal advice. about two months ago, whilst sat in stationary traffic, my car rolled into the back of another car (I was travelling at a maximum of 3-5mph as my foot slipped off the brake, no damage was caused to either vehicle) Today I have received a letter stating that the person is trying to claim for personal injury (amount unkown). I remember reading in the media that a physio in the UK had successfully challenged a similar claim. I am wondering if anyone is aware of any evidence around the minimum speed required to cause a whiplash injury, as I am keen to find out if i can challenge this claim, basically because I have a real issue with the compensation "where theres blame there's a claim" culture we now live in.

Any advice would be appreciated.