Hi Kamal, the rules say that you can't start an ATPL theory course unless you hold a PPL. The UK CAA have the most extreme interpretation of this which is that 'hold' means 'hold in your hand', ie issued and delivered. For that reason most reputable ATOs won't be able to start you off on a course at this stage of your PPL training. What I would suggest is that you get Paco's book in PDF
from here, very reasonably priced and up-to-date. When you do start a course you will find it useful as an alternative reference.