Peugeot 307 wont start

You will probably find the battery has a dead cell so it won't produce enough power to start the car but will still run the electrics. Try and use some jump leads on another running car and if that works replace the battery or at least get the battery checked with a high discharge meter.

Don't have the car that you are jump starrting yours off running, as you remove the jump leads it can create an electric surge and damage fuse box/ECU-very expensive!!!