paid less per hour when went part time - is that allowed?

[feb]

before i was pg i worked 50 hrs per wk. i cut down to 40 hrs per wk when pg. am salaried so my pay was reduced accordingly.
am trying to figure out how many hours i'd like to work, so requested my hr dept tell me what my hourly wage is. hr emailed me then sent me this:
'I've just spotted on your file that you reduced your hours to a 40 hour week before you went on maternity leave which reduced your gross pay.

The letter of 6 Nov 2006 from (the boss) confirms that your annual salary was reduced by £x gross per week, this will alter your hourly rate as follows:'

hourly rate went down. was doing exactly the same job, so are they allowed to do this?

feb
No they can't just reduce your hourly rate!
You say you are salaried, not paid by the hour?
If your contracted hours a week (i.e not the actual hours you worked) were previously 50 hours, then you reduced to 40 hours, doing the same job, the hourly rate should be the same.
Have you tried working it out yourself - they may be just miscalculating?
If you divide your previous salary by 50 then multiply by 40 that should tell you what your new salary should be - if that figure is what your new annual salary actually is, get them to check the hourly rate again, Sounds as though they may just be calculating wrong or something.
hope that makes sense!

thanks flowerybeanbag.
they've sent me some calculations showing how it is all worked out but i don't really understand it tbh!
definitely salaried.

if you want to CAT me the calculations they have given you (rather than share with the world!) I am happy to explain if I can?

think i have figured it out. she seems to have worked the initial figure out on a 45hr week rather than 50.
whichever way i look at it its hardly worth going back to work!
thanks for the offer tho.
x