The planned flotation of the trainline rail ticket website has been derailed by private equity giant KKR.

The US firm swooped yesterday to buy thetrainline.com from buyout firm Exponent for an undisclosed sum, heading off an IPO which could have valued the business at £500million. Exponent paid around £160m nine years ago to buy the venture from consortium owners including Virgin and Stagecoach which created the business.