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Standard insurance company practice (aka underhand dealing).
Your base premium is calculated on a number of factors (age, postcode, accident history etc.) and then once all this comes up with a price the NCD is applied. Your "risk" changed therefore the price went up.
Bear in mind not all insurers are the same. They may be dearer but IMHO the NFU can't be beat. I had a 110 stolen, they paid out 11.5k ukp (which is what I paid for it 2 years earlier) and when I went to insure the same model, but this time valued at 18k, the premium went down because my age had gone over a threshold into a lower risk group.
Any claims I have made have been 100% hassle free.
C