Offered a different role when I return back to work - what are my rights?

[Zuzusmom]

I plan to return to work after taking 8.5months for my beautiful daughter. Unfortunately it is a financially-led decision so I don't have much choice unless we were to uproot completely which I don't want to do.
My job is in advertising, so is very high stressed with big expectations to work outside of office hours. It is also quite a fluid industry - ie, your position is only safe if the client remains with the agency.
My client left the agency just as I went on mat leave, but I was told at a KIT day that they were pitching for new business and they were sure there would be a role for me when I come back.
I plan to start in a few months. I got a phone call today and they were offering me a role but a very specialist one which (although some skills are transferable of course) I don't feel is right. Plus I know from working in the agency that this client is a nightmare and everyone hates it.
At the moment they have posed the role as a choice, but there is no alternative to choose from. I need help to establish my rights for return. This role isn't suited for me but I worry they are pretending it is and hoping I say no because they have technically offered and therefore if I say no they have to pay less redundancy? What are my rights? I don't know where to begin searching. I feel so much anxiety about making the right decision - do I accept the role because it's better to have a job or do I reject the role and shoot myself in the foot further down the road?
To complicate things more... I plan to get pregnant in a year with second baby and need to remain in this agency for maternity pay, as won't qualify if I started a new job. Please help :(

[Hereforthebeer]

I am not a lawyer, and it sounds like you should see one. I know a couple of things which could help.. ask for the job spec, (as in a phone conversation you can't see the detail of the orle they offered). They are meant to offer you a suitable alternative. go through the spec line by line, if you are significantly not meeting what is needed for the role you have evidence that its not a suitable alternative. If you plan to get pregnant anyway i wouldn't have thought going back to proposed job (if it comes to it) would be ok? Unfortunately it seems a companies do this to women coming back from maternity and they can afford lawyers/HR experts.