Mortise Lock Replacement: Why & How to Upgrade Securely

Replacing a mortise (or mortice) lock with a 5-lever BS3621 version is one of the most effective ways to boost door home security and satisfy insurance requirements in the UK.

At ALS Locksmiths Glasgow & Paisley, we specialise in supplying and fitting high-quality mortice lock replacements across Glasgow, Paisley, Renfrewshire, and surrounding areas. Below, we explain when you should replace your mortice lock, what to look for, and how to avoid common pitfalls.

Why Replace a Mortise Lock?

• Insurance compliance — Many insurers require a 5-lever BS3621 mortice lock (or equivalent) on external doors.

• Improved security — Older 3-lever or worn mortise locks offer little resistance to forced entry.

• Wear and tear — Internal parts may degrade, misalign, or fail over time.

• Mismatch of components — If the new lock and old keep don’t match, the security can be compromised.

What Type of Mortise Lock Should You Use?

1. 5-Lever BS3621 Mortice Lock

• Full British Standard certification.

• Uses a “sash lock” format: combines latch (operated via handle) + deadbolt (key operated).

• Provides robust protection when fitted correctly.

2. 3-Lever Mortise Lock

• Simpler and less secure.

• May still be used internally or in low-risk areas, but not ideal for main external doors.

3. Deadlock Only (Mortice Deadlock)

• For doors without handles; only deadbolt operated by key.

• Risk: if used alone without a sash lock or proper alignment, pressure/force can jam the lock over time.

Key Considerations & Best Practices

• Replace the keep too — The metal strike/keeper must match the new lock; using an old keep can void BS compliance.

• Proper alignment — If the bolt pulls sideways, the internal “curtain” can detach, causing the key to spin without operating the lock.

• Avoid deadlock-alone on poorly supported doors — Without a striker or supporting hardware, force can strip or jam the mechanism.

• Handle + latch compatibility — Ensure the latch and handle mechanism work smoothly together.

• Secure materials — Anti-pick, anti-drill, hardened components help resist tampering.

When Is Replacement Needed?

🏠 Why Choose A.L.S. Locksmith

• 🧰 Domestic Locksmith Specialist – uPVC & composite door lock specialist, We install other locks too.

• 💷 Affordable Local Pricing – Clear, fixed prices, No Vat, Priced per job not per hour

• ⚙️ Repair-First Approach – We fix the mechanism before replacing it

• 🛡 Guaranteed Parts & Labour – All parts supplied and fitted come with a full warranty

• 📍 Local & Trusted – Hundreds of genuine ⭐⭐⭐⭐⭐ customer reviews

📞 Call to Action

Call A.L.S. Locksmith today for professional lock changes and security upgrades to protect your new home.