The cover people are most sure they have.

"Cancer" is not one thing in a policy

People buy this believing it pays out if they are told they have something serious. What it actually does is pay out if a doctor's diagnosis matches a definition written in the policy document — and those definitions are specific, staged, and vary between insurers.

A condition can be real, frightening, life-changing and still fall outside a particular wording because of how far it has progressed or which type it is. That is not an insurer behaving badly; it is what was bought. But it is why two policies at the same monthly cost can be worth very different amounts when something happens.

This is the single reason I will not quote this on price alone. Comparing two of these by premium is comparing two documents you have not read.

How many conditions, and does it matter?

Policies advertise a number — a list of conditions covered. The number is close to meaningless on its own. A long list padded with rare conditions is worth less than a shorter list with generous definitions of the common ones, and the common ones are what claims are actually made for.

What is worth checking is how the handful of conditions that account for most claims are defined, and whether the wording has kept pace with how those conditions are now diagnosed and treated.

Things that surprise people

• There is usually a survival period. A short window after diagnosis during which you must still be alive for the claim to pay. It is why this is not a substitute for life cover.
• Partial payments exist. Many policies pay a smaller amount for less advanced conditions, without ending the policy. That feature is worth more than a longer headline list.
• Children are often included. Sometimes at no extra cost, and a great many people have no idea it is there.
• It can be bought with life cover or on its own. Combined usually pays once, on whichever happens first. Separate policies usually cost more but can each pay out. Neither is right by default.
• It does not care about your credit file. Underwriting is health and occupation. A CCJ is generally irrelevant here.

Why claims may be declined

A critical illness claim must meet the terms of the policy. A claim may be declined if the diagnosed condition does not meet the policy definition, an exclusion applies, or another relevant policy requirement has not been met.

The information provided when the policy was taken out can also matter. Inaccurate or incomplete answers to application questions may affect a claim, depending on the circumstances and the applicable rules.

When applying, answer the insurer's questions fully and accurately. If you are unsure whether an investigation, symptom or previous medical consultation is relevant, ask the insurer or your adviser rather than guessing.

The aim is to understand what you are applying for and make sure the insurer has the information it has asked for, so you have a clear understanding of the cover and its limitations.

When I would say don't

If money is tight and you have to prioritise, I would start with the financial risk you most need to protect against.

Income protection is designed to replace part of your income if illness or injury prevents you from working and you meet the policy's terms. Critical illness cover pays a lump sum if you meet the policy definition for a specified condition. They address different risks, and neither is automatically the right priority for everyone.

If you already have meaningful cover through your employer, bring the policy details. We can look at what it provides, what limitations apply and whether there is a gap worth addressing.

And if you already have a policy, the useful first step may not be buying another one. It may be understanding the cover you already have.