From what I recall from a previous discussion on the forum about this type of issue, what the insurers will claim is that they will have 'reviewed' (upwards) your 'starting premium' but still applied the full 'no claims' reduction in line with your one claim not breaching the protected bonus rules (e.g. 2 claims in three years - yours may be different).

I had a similar event many, many years ago (admittedly the increase wasn't anything like what you face) and was given a similar response. Note that this time around, you also have the added pain of premiums generally rising to (IMHO) 'fund' insurers' inflationary costs and to some extent offset actual and potential high value claims for newer cars, especially for EVs.

Whilst EV owners (especially the higher valued ones) will bear most of the brunt, ICE car owners costs will increase through their fault claims being a lot more expensive. The same goes (though to a lesser extent) most modern cars, where they may be safer, but much more expensive to repair, especially on relatively minor accidents. All that extra gizmos to replace, expensive paint jobs, etc, etc. We're all getting dragged into this.

Insurance premiums generally (not just motoring) have gone up quite a bit since the start of the pandemic.

Was your claim a fault one on your side? If so, that may have been a big factor in them 're-evaluating' your risk. Sometimes that can be your general circumstances changing, just moving home, an insurer backing out of a type of person they wish to insure (by pricing people to move provider) or from one age bracket to another. This often applies to older drivers as they hit the 75 year old mark, as it did with my parents.

Even so, I'd shop around for alternative quotes (including on comparison websites) which may come in at much nearer (though likely still above) last year's one from your existing insurer. I suspect several factors are at play in your case.

They are trying to get the money they paid out back. Try other insurers to see if you can get a better deal. Insurers are there to make money and will try anything to ensure that objective is achieved.