The error that undoes more refusals than any other is late service. Employers treat the deadline as advisory, send the refusal a few days before the holiday, and discover that the counter-notice period had already expired, leaving the leave validly booked by default. The fix is mechanical : count the days the moment the request arrives, and serve any refusal well inside the Regulation 15(4) window. A close relative of this mistake is the oral refusal. A decision communicated in passing, by text or in a quick chat, carries no evidential weight and does not satisfy the statutory requirement to specify the days in writing, so it offers no protection if the matter escalates.
The second cluster of mistakes is about content. Some employers state no reason at all, which invites the inference that the refusal was capricious, while others say too much and stray into commentary on why the employee wanted the time, which is exactly the material a tribunal will scrutinise for discrimination. Keep the reason operational and brief. Never refuse a request tied to a religious observance, a disability-related need, or pregnancy-related leave without taking advice first, because what looks like a routine scheduling decision can become an Equality Act 2010 claim. Finally, employers forget to check the contract, apply the statutory default, and overlook a relevant agreement that set a longer notice period; the result is a technically invalid notice. The UK dismissal letter sits in the same family of decisions where getting the evidential trail right is what protects the business.