Yes. Current GOV.UK guidance states that you must report an accident to your insurance company even if you are not planning to make a claim.
Notifying the insurer and making an insurance claim are two different things. You may decide to pay for your own body repair, but that does not remove the separate reporting requirement described by GOV.UK or any additional notification requirements contained in your policy.
GOV.UK also states that where an accident causes damage or injury, the required details should be provided to someone with reasonable grounds for requesting them. If those details are not exchanged at the time, the accident must be reported to the police within 24 hours.
You can review the current official information at GOV.UK — If You’re in an Accident.
Once the incident has been reported, whether you proceed with an insurance-funded repair depends on the circumstances, policy and repair cost. If you intend to claim, ask what information the insurer needs before any work is authorised.
Our guide What to Do After a Minor Collision covers the practical steps after an incident, while How Car Insurance Repairs Work explains the later claim and repair stages.