The Electoral Commission has published the second stage of its guidance for campaigning around the EU referendum, covering donations, loans and donor permissibility.
Updated guidance on ‘Campaigning and registering for EU referendum campaigners’ (pdf, 235KB) also includes information for charities who are considering whether to register as campaigners. This appears to be the relevant paragraph (on page 8):
Charities can register as referendum campaigners if they are eligible to register and the rules on the referendum will apply in the same way to charities as for all other campaigners. However, referendum campaigning, or political activity must be undertaken by a charity only in the context of supporting the delivery of its charitable purposes. Before you decide to register as a campaigner you should read the guidance on campaigning and political activity issued by your charity regulator to ensure that as a charity you can properly undertake referendum campaigning in accordance with charity law.
Note: VoluntaryNews coverage to date now should have an EU referendum tag.