US Postal Money Orders cashed or deposited in UK?

I have received two US Postal money orders from my daughter in the US.  I thought it would be no problem to deposit them into my Natwest bank account.  However, I got a phone call from the bank today informing me that they do not accept them.  They are going to post them back to me.  She did tell me that she thinks the Post office will cash them.  Does anyone know if they will? 

I think they will if it's an  international money order otherwise I don't think they can. I would try a bureau de change or a bank with an international counter.