I may be wrong, but I think it works like this with 'new' unwritten contracts.
If when they first put the notice up/sent the memo around, if no one questioned it then, and everyone just followed it, it will after a period of 6 months (I think) become part of your working contract. However if when they first told everyone, everyone said hang on a minute, this is not going to work, then the new 'contract' should be null and void.
It works on the basis of any new contract has to be approved by both parties (i.e. employer and employee), otherwise for instance a new company could form, with the best working conditions in the world, then 6 months later decide that they can't afford to carry on supplying Ferrari's as run-arounds, and instead of having 5 scheduled breaks in the day they could revert back to just your lunch break, if the employees go along with it, then it is as good as saying they accept the new conditions, if they don't go along with it, the original contract will stand.
Please bear in mind though that if you put your foot down on something that the company is really wanting to happen, you may find that you are out on your ear, they can't sack you for not agreeing to the new contract terms, but as we all know there is more than one way to skin a cat (or so I am told!!!)
Having said all of that, I believe that everyone is entitled to 4 weeks holiday a year (a week of his may HAVE to be taken at Christmas), and that everyone is entitled to take their holiday as and when they please. HTH