Astra twintop push button start, central locking not working ?

Hi
Please can you help me ?
I have hired the answers on this forum but I don't have an ignition barrel as it's push button start.
For the past few weeks my central locking has been acting up, however once I am in the vehicle
I have no issues in starting it.
Today I locked the car and all was ok until a good few hours later the chap over the road knocked on my door and advised my lights had been left on!!!!
The lights are automatic and should turn off when I unlock the car
The car was Definatly locked
I managed to open the vehicle with no issues, however the car wouldn't start.
I know this has got to be a flat battery
Due to the lights been left on,
I now have that charging.
I am stumped as to what this could be and was hoping someone could help me ?
I don't think it's the car battery as it's the central locking I have experienced the issue with and the car has been starting fine.
Hope someone can help ???