If we have 'duvet days' do they come off our annual leave?

You are supposed to present yourself fit for work. If you had a rough night, or you feel like a little self-indulgence and want to have a 'duvet day', that comes off your annual leave or flexitime arrangement. 'Duvet days' are just a mechanism that some employers may offer to let you take your annual leave at shorter notice than you may normally have to give. This shouldn't be confused with taking a day off sick when you actually are too ill to come to work.