Land Rover Freelander some times wont start

this problem has just started, starts first time nearly every time, but twice this week after leaving the car for about twenty mins when i turned the key it did not start it just went to start but did not pick up after a few mins it just started,then drives perfectley then after a few days it will do the same again,i may have driven hundreds of miles before it does it, no problem first thig in morning.i have tried to make it happen by switching of waiting a few mins and then start, but it starts ok,the car has regular services,the last only 2000miles ago,but i know it going to let me down at the wrong time. thank you.