I would go for clothes bank, there is a charity that specialises in sending them overseas, there is trade in second hand clothes going from UK to be sold in Africa I believe and I'm sure I saw a thing saying bras were good for that.
Just googled, OXFAM, http://www.oxfam.org.uk/donate/the-big-bra-hunt
Didn't know where to put this, so apologies if this isn't the right place, but hoping someone will help me. I have some maternity bras and breastfeeding bras that I don't need anymore. I sthere a charity or will local hospital appreciate them? I'm assuming a charity bag isn't the right place for them?