Insurance claims involving illness or injury almost always need medical evidence. Here's what UK insurers actually require, and how to avoid claim delays.
Medically reviewed by Dr Sulaiman Shah , MBChB BMedSci, MRCGP — General Practitioner and founder of The GP Clinic. Last reviewed: 16 September 2026
Quick answer: A medical letter communicates information — it’s written by a healthcare professional to a specific person or organisation, often with flexible content. A medical certificate verifies something — a standardised document confirming a health status or fitness for a specific activity, usually with legal or administrative weight. They’re related, but not interchangeable.
In the medical field, there are various types of documents that serve genuinely different purposes, and medical letters vs medical certificates is one of the most common points of confusion patients run into. Understanding the difference means you ask for the right document the first time, instead of finding out too late that what you have isn’t what’s actually required.
Medical letters are written by a healthcare professional and addressed to a specific individual or organisation — another clinician, an employer, a university, an airline. Their purpose is to communicate information, explain a medical situation, or request a specific action, such as a workplace adjustment or academic extension.
Medical certificates are official documents that verify a person’s health status for a defined purpose — most commonly, confirming fitness (or unfitness) for work, in the form of a fit note. They exist to provide standardised proof, not to explain the full clinical picture.
Medical letters vary considerably in format, since they’re tailored to their recipient and purpose. A letter might include the patient’s history, the reason for referral, or specific recommendations — as much detail as the situation genuinely requires.
Medical certificates follow a far more standardised format. A UK fit note, for example, includes the clinician’s details and registration, the assessment date, a general statement on fitness for work, and the certified period — not a detailed diagnosis. That last point is worth being precise about: a standard certificate is designed to confirm fitness, not disclose your full medical history to whoever receives it.
| Medical Letter | Medical Certificate (e.g. Fit Note) | |
|---|---|---|
| Purpose | Communicates information or requests an action | Verifies fitness/unfitness for a specific activity |
| Format | Flexible, tailored to recipient | Standardised |
| Typical recipient | A named individual or organisation | Employer, school, insurer, authority |
| Diagnosis included? | Sometimes, if relevant and consented to | Not by default |
| Legally required for absence? | No | Often yes, beyond 7 days’ self-certification |
| Common examples | GP referral letter, fitness-to-fly letter, university mitigating circumstances letter | Fit note, private medical certificate |
Medical letters are commonly used for referrals, requests for specific accommodations, or communication between clinicians and third parties. They don’t carry a fixed legal status themselves, but their accuracy still matters — a letter supporting a university mitigating circumstances claim, for instance, needs to be precise and genuinely reflect the assessment.
Medical certificates carry more defined legal weight. A fit note is the standard evidence supporting Statutory Sick Pay claims and workplace absence policies once self-certification no longer applies. Providing false or misleading information on a certificate is a serious matter, since employers, insurers, and institutions rely on it as accurate evidence.
Medical letters can usually be verified by contacting the healthcare provider named in the document directly — recipients can cross-check the clinician’s details and credentials if authenticity is in question.
Medical certificates typically carry the issuing clinician’s registration details and, where applicable, a signature or official stamp. Employers, insurers, or authorities can verify authenticity by contacting the issuing clinic, and for online services, checking the clinician’s GMC registration is a reliable independent check.
Medical letters and medical certificates aren’t different names for the same thing — a letter explains, a certificate verifies. Asking for the wrong one wastes time and can leave you without the document an employer, school, or insurer actually needs. If you’re specifically trying to understand what goes into a UK medical certificate and what stays private, that’s covered in detail separately — the short version here is: know your purpose first, then ask for the document that matches it.
Usually not for standard sickness absence beyond 7 days — most employers specifically require a fit note (a type of medical certificate) rather than a general letter, since it follows a recognised, standardised format.
No. Medical letters can be written by GPs, hospital doctors, or other appropriately registered healthcare professionals, depending on who is best placed to address the specific situation the letter covers.
Not really — a certificate is deliberately standardised and brief, while a letter is meant to explain context in more detail. If you need both confirmation and explanation, you may need both documents.
Only what’s proportionate to its purpose and what the patient has consented to share. A letter requesting a workplace adjustment, for example, doesn’t need full clinical history — just enough for the recipient to understand and act on the request.
Not in the same way a certificate can be. A letter is a professional communication, and while its accuracy matters, it doesn’t carry the same standardised legal weight as a certificate used for statutory purposes like sick pay.
Sometimes, if you need more explanation than the certificate provides — for example, a certificate might confirm you’re unfit for work, while a follow-up letter explains specific adjustments needed for your return.
Many universities specifically request a letter for mitigating circumstances processes, since they need context and reasoning rather than just a standardised fitness statement — check your institution’s exact policy, as requirements vary.
The employer can contact the issuing clinic or clinician directly to confirm authenticity, and for online services, checking the clinician’s registration (GMC or equivalent) independently is a reliable way to verify legitimacy.
