I cannot think of any school in the UK that requires students to have O levels, before joining their routine "pay your money and take your chance" courses.
In the "very rare" cases where places are sponsored by airlines the sponsors will probably specify some minimum qualification standard.
So just go to the UK CAA website and do a search for schools authorized to carry out ATPL courses.
A potentially greater problem is the fact that student VISAs for entry into the UK, will only be provided for study at those schools which are on the approved list of student VISA sponsors. If a school does not have the approval you will not get a VISA. So don't pay any money to any school before first ensuring that you will be able to get a VISA.
Last edited by keith williams; 15th Aug 2014 at 17:11.