Inside is my best attempt...
You do not necessarily have the right to choose when you take your holiday, and your employer can tell you when to take your leave.
However, your employer has to give you 2 days' notice of this for every day they want you to take. So if your employer is telling you that you must take 4 days' holiday, they need to give you 8 days' notice of this.
Your employer can refuse your request for a specific holiday date, but you cannot turn down your employer's instruction to take leave if they give you the correct notice.
This is not very fair, but it is not that common for employers to do this.
Many more employers are likely to have rules about when you can take leave - for example they may forbid leave at busy times of year (such as the run up to Christmas) have a system that ensures that critical tasks are always covered or simply reserve a right to say no to individual requests.
Some restrictions are not unreasonable, but they should not be operated in a way that discriminates unfairly. And it is good practice for employers to make the rules as clear as possible, to have a clear justification for them and operate them consistently and fairly.
Your contract of employment, staff handbook or intranet should have further details