From the CAB website, pay attention to paragraph 3...:
Can you choose when to take holiday
You can ask to take your holiday whenever you choose, as long as you give your employer the right notice and take into account certain agreements between you and your employer. However, an employer has the right to refuse your request to take holiday, as long as they give you the right notice at the right time and take account of certain agreements between you.
Your employer can order you to take all or any of your holiday at a particular time, as long as they give you the right notice at the right time and take into account certain agreements between you.
The law does not put any limit on the amount of holiday you can take at any one time. This means you are not entitled to take two weeks of holiday at once, unless your agreement or employment contract says you can. This means that as long as an employer gives their employee the right notice at the right time, they could make you take your holiday as they choose, for example, take every Friday as leave until you have used up all of your holiday.