I have two MS Outlook accounts, one for work and another for an organisation I volunteer for. Both have 'UK Holidays' added. However, my work calendar is incorrectly showing May 30th for the Spring Bank Holiday, which was moved to 2nd/3rd June. The other calendar is fine, which makes me think it's probably a local issue (I've reported it to our Service Desk, but I'm curious enough to look into it myself too). I've tried deleting and re-adding the uk holidays, but it didn't help. There are other people online reporting the issue to Microsoft via their forums, so it seems to be a common problem.
Is your Outlook calendar correct?