2003 Mini Cooper S Starting Trouble in Hot weather.

I drive a 2003 Mini Cooper S and now for the second time my car has failed to start. Both times this has happened the weather was very hot (I live in Cape Town S/Africa) and after the first time I had the battery checked and all was OK. The car started perfectly all day on both occasions and all of a sudden when you try to start it you just hear a clicking sound, maybe five or six clicks and then nothing. I had to push start it both times after which it is fine. Very strange. Any suggestions?