i don't know the law here, but we have had loads of changes recently - the holiday year, pay dates, salary review dates and all came out as announcements on the company intranet (apart from the pay dates, they went as letters to the affected staff first then intranet)
with immediate effect xxxx will be changing to YYY - except the salary pay dates, those affected were given 3 months and an offer of a bridging load before that one comes into effect.
no consultations were done & they are a massive company, everything employment wise gets run past the legal team