This is a terrible HR faux-pas by the employer.
What a reasonable employer should have done (if there is a short-notice problem) is to sit down with all the staff, explain the problem, ask for suggestions as to how to get around it. That would be on the basis of providing cover over this 'special' weekend of Queens Diamond Jubilee
But it sounds like your whole roster (for everyone?) has been shifted about?
In the first instance, is there anything in your Employers' Handbook or other employer-issued documentation about the employees' need to change patterns at short notice?
If nothing, your legal right is probably that you could refuse on the grounds that less than contractual notice has been given - unless it is custom and practice in your industry that this sort of thing happens? (For example, fishermen have to be rostered to start when the tides are OK - and that is accepted in that industry).