A. The Working Time Regulations permit you to have a total of 28 days’ paid holiday per year but other than bank holidays and public holidays, which are fixed, the employer needs to approve the dates for the holiday you have requested. You cannot demand to have four consecutive weeks but the employer should explain why he is refusing.
If he has permitted other employees in the past to have four weeks off he may be acting unreasonably or inconsistently in refusing your request. No doubt the employer has given a detailed explanation for the refusal as he has to balance your ability to have paid leave with the requirements of the business to provide its services to its customers.
Generally, employers are more likely to consent to extended periods of paid absence where it is not within peak holiday time or where it may bridge business close down either in the summer or over the Christmas and New Year period, as that will clearly have less impact on you being away.
If you are aggrieved you could raise a formal grievance.