Critical illness cover is an insurance policy that pays out a lump sum if the policyholder is diagnosed with a serious illness specified in the policy terms, such as certain cancers, a heart attack, or a stroke.

It’s often taken out alongside a mortgage, since a serious illness diagnosis can affect a household’s ability to keep up with repayments, though critical illness cover is a separate product to life insurance and to income protection, and pays out only for the specific conditions listed in the policy, not for every illness or injury. Policies vary between providers in terms of which conditions are covered and how they’re defined, so it’s worth comparing options and getting advice on what level of cover is appropriate for your circumstances.

How Critical Illness Cover Is Underwritten and Claimed

In short: a critical illness policy pays out on a defined list of conditions, at a defined severity, after a defined survival period, and those three definitions decide almost every claim. Two policies can both say they cover “cancer” and still behave very differently, so the wording matters more than the headline list of conditions.

Condition definitions and severity thresholds

Insurers describe each condition against a clinical threshold rather than a plain-English label. A heart attack, for example, is usually defined by evidence of cardiac enzyme changes alongside symptoms and ECG findings, not simply by the diagnosis appearing in your notes. Many insurers also pay a reduced amount for less advanced conditions, often called partial or additional payments, which can pay a percentage of the sum assured without ending the policy.

The survival period

Most policies require the policyholder to survive a set period after diagnosis, commonly 10 to 14 days, before the lump sum becomes payable. This is a routine feature rather than a trap, but it is one reason critical illness cover is often arranged alongside life cover rather than instead of it, so that a household is protected in either outcome.

Disclosure at application stage

Applications are medically underwritten, which means you answer questions on your health history, family history, smoking status, height and weight, and occupation. Your duty is to take reasonable care not to make a misrepresentation. If your GP records are later requested at claim stage and contradict what was disclosed, the claim can be affected, so it is better to over-disclose an investigation or a symptom you were unsure about than to leave it out.

How it sits alongside a mortgage

Cover is often written on a decreasing basis to track a repayment mortgage, or on a level basis where the borrower wants a fixed lump sum regardless of the outstanding balance. Interest-only borrowers generally need level cover, because the capital balance does not reduce over the term. Whether the policy should be written in trust, and who the beneficiaries should be, is worth discussing before the policy starts rather than afterwards.

Read our fuller guide to critical illness cover, compare it with our income protection insurance guide, and see how insurers apply the definition of a smoker for life insurance. You can browse everything in our mortgage, property and money advice hub, meet our advice team, or return to the Needing Advice homepage.

How critical illness cover works alongside a mortgage

Critical illness cover is not a condition of getting a mortgage in the UK. No lender can require it, and it is a separate decision from the mortgage itself. What it does is protect the repayments: if you are diagnosed with a condition listed in your policy and you survive the policy’s survival period (commonly 14 days), the insurer pays a lump sum you can use to clear or reduce the outstanding balance.

Decreasing versus level cover

Cover is usually arranged in one of two shapes. Decreasing cover is set up to fall broadly in line with a repayment mortgage balance, so the sum assured reduces over the term; it is the cheaper option and is designed to clear the debt rather than leave a surplus. Level cover keeps the sum assured fixed for the whole term, which suits an interest-only mortgage, where the capital balance does not reduce, or anyone who wants a lump sum left over after the mortgage is settled.

What affects whether a claim pays out

  • The condition must be listed, and must meet the policy definition. Policies pay on defined severity, not on the name of the diagnosis alone — this is the single biggest source of declined claims.
  • Disclosure at application. Non-disclosure of medical history or smoking status at the point of application is the second most common reason a claim fails.
  • Number of conditions covered varies widely. Providers differ substantially in how many conditions they list and how generously they define them, which is why the cheapest quote is not automatically the one that pays.
  • Children’s cover and additional payments are included as standard on some policies and are an optional extra on others.

How it differs from the two products people confuse it with

Life cover pays on death (and usually on terminal diagnosis) and pays nothing if you recover. Income protection replaces a proportion of your monthly earnings while you are unable to work, for any medical reason, and pays monthly rather than as a lump sum. Critical illness cover sits between the two: a one-off lump sum, payable while you are alive, but only for the specific conditions named in your policy. Many households arranging a mortgage combine critical illness cover with life cover on a single policy, which is generally cheaper than two standalone plans but pays out only once.

Related Guides

Looking for in-depth coverage options? Read our full Critical Illness Cover Guide for details on claims, definitions and choosing the right protection.