If your car is worth more than its standard market value — because of a performance build, rare specification, or collector status — standard car insurance will leave you underinsured at total loss. A stock Ford Mustang GT might be worth £25,000 on the market. With £18,000 in engine and drivetrain work, the car may be worth £45,000+. A standard policy pays the former. An agreed value policy pays the latter. According to Hagerty’s Classic Car Market Report, 68% of modified and collector car owners are underinsured by at least 30%.

What Is Agreed Value Insurance?

Agreed value (also called guaranteed value) insurance is a policy where you and the insurer agree on the car’s total value before the policy starts. If the car is declared a total loss, you receive exactly that amount — no depreciation, no market value argument, no negotiation. This is different from stated value, where the insurer pays the lesser of the stated amount or actual cash value.

How to Get an Agreed Value Policy

1. Document the car — photos of every modification, receipts, build sheet, dyno sheet
2. Get an independent appraisal — a professional written appraisal from a recognised automotive specialist supports your claimed value
3. Approach specialist insurers — Hagerty, Grundy, American Collectors, Heacock Classic, and specialist UK brokers offer agreed value policies for modified and collector cars
4. Agree the value upfront — the insurer will review your documentation and either accept your proposed value or negotiate

What Documentation Do You Need?

• High-resolution photos (minimum 20, covering all angles and engine bay)
• Receipts for all major modifications
• Dyno sheet if the car has been performance-tuned
• Professional written appraisal (required by most agreed value insurers)
• Vehicle history check

Cost of Agreed Value vs Standard Insurance

Agreed value insurance for a modified car typically costs 20–40% more than a standard policy on the same car — but the protection is incomparably better. For a car with £30,000 in modifications, the difference between standard and agreed value cover at total loss could be £25,000+. The additional premium is almost always the better financial decision.

When to Review Your Agreed Value

Review the agreed value every time you make significant modifications, at a minimum annually. If you’ve added £5,000 in parts since your last policy review, your car is underinsured by that amount. Most specialist insurers process mid-term value increases for a small admin fee.

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