Louise Foster is now battling to overturn Lancashire CC's decision in March last year refusing her son, James, a place at Highfield High School, opposite their home.
Mrs Foster had indicated Highfield as her first-choice school for James in December last year but competition for places at the school was high and because it was over-subscribed the CC implemented its policy of giving priority to children whose primary education had not been in a Roman Catholic school, the court was told.
James, who was taught at Our Lady of Assumption Roman Catholic Primary School, was refused a place at Highfield and was offered one at St Mary's High School instead.
'This council imposes a restriction on certain parents defined by religious affiliation which is contrary to and inconsistent with the Act,' Mr Bradley said.
The court heard that in July last year the department of education had asked the CC to review its policy because 'it took the view that the policy was not justifiable on educational grounds.'
But the following October, after consultation with Roman Catholic church authorities, the council decided to maintain its existing policy.
'It cannot be right that because of the religion of the child and parent their preference is placed those of all other parents,' Mr Bradley said.
Mrs Foster had 'exercised her rights under a scheme Parliament has given her to enable to express her preference the same as any other person.'
The CC firmly denies its policy is unlawful. Its barrister, Mrs Elizabeth Appleby QC, told the court that the council 'can have any reasonable admissions policy they think fit.
'The council's duty under the Education Act is to make arrangements to enable a parent to express a preference. There is no duty to make arrangements which will give parents the school they wish for,' Mrs Appleby said.
'A sibling connection, medical reasons, geographical proximity or feeder primary schools are valid criteria in the case of over-subscribed schools. The Act does not preclude any criteria applicable in the case of an over-subscribed school related to religion,' she told the court.
The judgement is due today.