Don't worry about the scoring system - the whole point is, as a woman on maternity leave, the scoring system should not apply to you anyway.
If there is a pool of 4, and there are 2 posts available, at least one of which is suitable for you, you must be offered it. Simple as that. You can't be made to compete with other members of staff in a pool. If there's a job there, it's yours.
I'm sure they are following their own policy, but there is no policy in the world that contains every single bit of legislation relating to a subject.
Write back to them quoting the following passage from the Equality Human Rights website:-
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"If an employee on maternity leave is to be made redundant (for whatever reason) and there is a suitable available vacancy, the employer must offer it first to the woman on maternity leave. This is a rare case where legislation requires a form of positive discrimination. If an employer does not comply with regulation 10 of the Maternity and Parental Leave Regulations 1999 (MPLR) an employee will have a claim for automatically unfair dismissal under the ERA s 99.
Regulation 10 of the MPLR 1999 states:
This regulation applies where, during an employee's ordinary or additional maternity leave period, it is not practicable by reason of redundancy for her employer to continue to employ her under her existing contract of employment.
Where there is a suitable available vacancy, the employee is entitled to be offered (before the end of her employment under her existing contract) alternative employment with her employer or his successor, or an associated employer, under a new contract of employment which complies with paragraph (3) (and takes effect immediately on the ending of her employment under the previous contract).
The new contract of employment must be such that -
a the work to be done under it is of a kind which is both suitable in relation to the employee and appropriate for her to do in the circumstances, and
b its provisions as to the capacity and place in which she is to be employed, and as to the other terms and conditions of her employment, are not substantially less favourable to her than if she had continued to be employed under the previous contract."
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So, if they don't follow Regulation 10 of the Maternity and Parental Leave Regulations 1999 as above, you will have a claim for automatic unfair dismissal under the Employment Rights Act 1999.
Then quote the following:
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"An employee who is made redundant whilst on maternity leave will also have a sex discrimination claim:
-if there is not a genuine redundancy situation but it is used as a pretext to dismiss her for reasons relating to her absence on maternity leave or because she has a baby. It may be difficult to prove this unless, for example, her job (or similar job) has been given to someone else; or
-if she is excluded from the normal redundancy procedure, such as being consulted, due to being on maternity leave, or
-if she is made redundant when there was a suitable available vacancy which, but for her maternity leave she would have been transferred or promoted into. "
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In other words, if they give your job to someone else as part of a redundancy programme, and, should you not have gone on maternity leave you would not have been made redundant (because you would have been placed in that job), then you have a sex discrimination claim as well. Here is the page with those passages.