I'm afraid you are completely wrong.
The 1944 Education Act was repealed in 1996. Section 25 was repealed even earlier - 1991. It therefore doesn't matter what it says. It isn't the law any more. But, even if it was, it doesn't say what you think it does.
Subsection 25(4) gives parents the right to withdraw their child from religious worship and/or religious education. That right is absolute and unqualified. It does not require parents to do anything other than tell the school what they want.
Subsection 25(5) deals with the situation where the parent wants their child to receive religious instruction of a different kind to that provided by the school, the child cannot be sent to a school that provides that kind of religious instruction and the parents or the LA have arranged for the child to receive religious instruction elsewhere. In that situation, it allows the parents to take their child out of school at the beginning or end of the day to receive that religious instruction. That is in addition to the rights given by 25(4).
The important point is that 25(5) only applies when the conditions in 25(5)(a), (b) and (c) are met. If those conditions are not met, 25(5) does not apply but 25(4) continues to apply.
The law today is set out in the School Standards and Framework Act 1998, section 71. Subsection 71(1) provides that parents can withdraw their child from religious education. As with the 1944 Act, that right is absolute and unqualified. It also allows sixth form pupils to withdraw themselves. Subsection 71(3) and 71(4) broadly echo subsection 25(5) of the 1944 Act, allowing parents who want their child to receive a different type of religious education to that provided by the school to take the child out of school at the beginning or end of the day to receive that religious education.