Yes. The notice period in your contract is binding on both sides. You committed to giving the employer that much warning before leaving; they're entitled to it. They can require you to work the full notice unless they offer PILON or garden leave, or unless you negotiate something shorter. Refusing to work the notice is a breach of contract, even if practical consequences are usually modest.
Notice periods are mutual contractual obligations. The clause cuts both ways: the employer must give you notice if they want you to leave (or pay PILON for the same value), and you must give them notice if you want to leave. There's a statutory floor (one week on either side once you've been employed for a month, scaling up to twelve weeks for the employer once you have twelve years' service) and a contractual figure that's usually higher.
The reason this exists is operational predictability. The employer needs time to recruit a replacement, hand over your work, and avoid disruption. The employee needs time to find a new role, prepare to leave, and avoid a sudden income gap. The notice clause balances those interests. Longer notices appear in senior or specialised roles where the disruption from a sudden departure is higher.
The employer's right to the full notice is enforced by contract law rather than by anything dramatic. They can't physically prevent you from leaving; what they can do is refuse to pay you for any unworked portion, withhold reference cooperation, and (rarely) sue for damages. The damages route is limited to actual losses caused by your premature departure, which are often small once you account for what the employer would have spent on you anyway.
In practice, most employers don't fight notice walkouts. The cost of replacing a leaver in three weeks rather than four is usually marginal, and the management time to enforce it isn't worth it. But the contractual position is firm. If your employer chooses to enforce the notice, they have grounds, and senior or specialist roles are the ones where enforcement is most likely.
There are three routes for the employer to vary their right to your full notice. Agree to a shorter notice (the most common). Pay PILON to end employment immediately while compensating you for the unworked period (clean and common in competitive exits). Put you on garden leave (keeps you employed but at home, so the notice still runs but you're not in the office). All three end your employment cleanly; the difference is the date and the cash.
If you're trying to leave earlier than the contractual notice and the employer says no, you have limited options. You can offer to find your own replacement (rarely accepted but sometimes works). You can propose a phased handover so the employer gets the operational value of the notice in a different shape. You can offer to take less PILON or no PILON in exchange for an earlier release. You can accept the date and serve the notice.
If something serious is happening that makes working the notice untenable (harassment, unsafe work, fundamental breach of contract on the employer's side), the rules change. You may be able to argue constructive dismissal and walk without consequence. This is fact-sensitive and you should take advice before relying on it. The threshold is high; ordinary unhappiness with the role doesn't get you there.
Practical recommendation: if you want to leave earlier, ask the manager first, propose a specific date, explain the operational handover, and don't move on until you have something in writing. If the answer is no, work the notice. The cost of breaching is usually small but real, and the cost of asking is nothing.
General information about UK employment law. For your specific situation, contact ACAS or an employment-law solicitor.