No. Insurance companies look at many things when pricing your insurance, especially your claims history. So, if you make a claim, your main policy price may still go up.
Protected NCD is there to protect your NCD. This means, that whilst your policy price may increase after a claim, if you have protected NCD, your discount would be protected and applied to the policy. This would still make it cheaper than without the cover.
It's important to know that there is a limit to the number of claims this can cover in a certain time. At Policy Expert, we allow for two fault claims to take place in a 3 year period per policy.
For more information check out our full article from the Know Your Policy series: Understanding how to protect your no claims discount.