All schools have to be open for a minimum of 190 days per year but all teachers have contracts for a minimum of 195 days per year, with the remaining 5 days being In-SErvice Training Days.
They're hardly new, as they were introduced (as part of new contractual arrangements for teachers) 30 years ago by the then Education Secretary, Kenneth Baker.
They were originally known as Baker Days, which often got shortened to B-days (bidets), on the grounds that teachers viewed them as something totally foreign, which they'd no idea what to do with ;-)