Maternity pay on a four/five day week

[Mishmishmish]

Been pondering this one - my company does a six month full pay maternity package. I've been with the company a very long time. When I came back to work 2.5 years ago I had arranged (via email/verbally) that I would work four days a week instead of five. Because of that my salary was pro rata-d so that I receive 4/5ths of my salary. My contract/salary hasn't changed or anything and the four days a week arrangement isn't in writing.
I'm pregnant and will go on leave again in the autumn. I'm wondering if the full pay I'll receive for the first six months will be based on five days a week or four. Anyone know how it works?
Thanks!

Why would it be based on five days a week? You don't work five days a week. If they paid you for five days a week while on maternity leave, that wouldn't be full pay, that would be 120% of full pay.

Yes the change to your terms and conditions 2.5 years ago should have been confirmed in writing (although you seem confused about that as you mention email as well as verbally), but as you've been working those hours for that salary for 2.5 years there's no way you can argue that it's a temporary arrangement and that you are contractually entitled to increase to 5 days whenever you like.

Ok thanks. I meant by email as in very casually, just a quick exchange to check it was ok, don't even know where those emails are. I guess I was confused about it because my official salary is still reflecting a five day week when I work four. It's not something I want to argue about with them, just didn't know what the situation was.

Also on the entitled to increase to 5 days whenever you like, yes I can - they said whenever I want to increase is fine with them.

How 'casual' the email was makes no difference at all. Anyway, the fact that you requested those hours and have been doing them for 2.5 years makes them contractual. Your 'official' salary isn't a historic figure you used to earn when you were doing different hours, it's the actual salary you earn now.

if you have it in writing that whenever you like you can increase your hours again, and you want to get a five day salary when you are on maternity leave, then I suggest you exercise that right and increase your hours back up to full time.

if you do that, check the terms and conditions of your maternity policy to see when 'full pay' is actually calculated, is it the day before your leave starts, or is it at some earlier period. Often the same reference period as for SMP is used, as many women reduce their hours late in pregnancy.