Hi I was hired to work for boots as a Christmas temp. It's 20 hours a week but need to lower it to 10 hours a week after 2 months am I allow?

I remember working retail part time in the summer hours 20 hours and the naturally reduced it to 10 hours because of lowered demand. Don't think you'll need to ask because you'll probably end up with 10 hours.

Do you really think that anyone on this International site will know?
tell you what.
Nip out on your High street and ask the people walking up and down the road.
Yes I am being sarcastic.

You can certainly ask for the reduction, but keep in mind they may just let you go because they hired your to work 20 hours.

By then it will be January, most stores are typically slower after the holidays. If they decide to keep you on then you may see less hours any ways. Wait and see how things go after Christmas. If you have to talk to your boss after the holidays and let them know you will need less hours.