If it's not a similar job they don't have to offer it to you.
If there is what is called a suitable alternative, they have to offer it to you. What constitutes a suitable alternative is very subjective obviously, but one which involved different skills, changes in pay, status, working environment or location would probably not be considered 'suitable alternatives'. You will be able to form an opinion whether this other job would be a 'suitable alternative' or not, but just being at the same level as your old job doesn't make it suitable.
Here is what it says on the DTI website about this -
'If a redundancy situation arises at any stage during an employee?s maternity leave which means it is not practicable for the employer to continue to employ her under her original contract of employment, she is entitled to be offered (before that contract ends) a suitable alternative vacancy, where one is available. This includes a vacancy with an associated employer or with a successor to the original employer.
The new contract must take effect immediately on the ending of the original one and must be such that:
the work to be done by the employee is both suitable and appropriate for her to do in the circumstances; and
the capacity and place in which she is to be employed and 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 original contract.
It is unlawful for an employer to make an employee redundant during ordinary or additional maternity leave period without first complying with these requirements. An employee made redundant in these circumstances will have a claim for unfair dismissal and may also be able to claim sex discrimination. An employee who has been dismissed in this way should appeal against the dismissal as part of the requirement under the Statutory Dispute Resolution Procedures. Failure by employers or employees to use these statutory procedures could result in an increase or reduction to any compensation awarded. The Acas Code of Practice on disciplinary and grievance procedures sets out the statutory dispute resolution procedures that should be followed before an employee may, if the dispute is not resolved, complain to an Employment Tribunal. Employers and employees may also find the general Acas advice on dispute resolution helpful.
If the employer has a suitable alternative vacancy available but fails to offer it to the employee, the redundancy dismissal will be regarded as an unfair dismissal. If the employer offers the employee a suitable alternative vacancy (she is entitled to a four- week trial period in which to decide whether the employment is suitable, and this period may be extended beyond four weeks by written agreement) and she unreasonably refuses it, either before or during the trial period, she may forfeit her right to a redundancy payment'.
So as you can see, if there is a suitable alternative for you, they must offer it to you without any competition.
If there isn't a suitable alternative, you don't get any further special protection due to your maternity leave - you can be made redundant the same as anyone else.
Out of interest, the job you have been offered - you say it is at a lower level - would they agree with that? And are they proposing protecting your salary?