Assuming this feminist group is one of the generic feminist groups, and not the feminist wing of (e.g.) banned far right group Scottish Dawn, this is actually a very big deal.
The bank has declined banking services to an organisation who they disagree with.
Question would be whether they would also decline services to the members of that organisation- if not, why not? probably because their compliance dept would implode at clear breach of Equalities duties to individuals
I'm not knowledgeable enough on business banking nor Equalities duties when providing services to business/charities/orgs to say if they've broken a rule by doing this, but might have a rummage in the regs later.