The way the BBC words that last paragraph, it sounds as if the minimum could be 3 years. What they mean it that some people have suggested a maximum of 3 years, and others have suggested a maximum of 10. From the consultation document it links to:
However, the point was made in the Parliamentary debate on the amendment that the current level of maximum penalty for an aggravated dog attack of 2 years imprisonment is too low, given the devastating effect that dog attacks can have on peoples lives and on assistance dogs. Overall, there is a range of possible maximum sentences between 2 years imprisonment and life that might apply in different circumstances.
In responding to this survey, please note that the Government is considering the
maximum sentence for these aggravated offences only. In sentencing, the court will have regards as usual to any mitigating or aggravating factors and it is anticipated that only the most serious of offences would result in a sentence towards the new maximum. Any change would be followed by a review of sentencing guidelines by the Sentencing Guidelines Council.
https://consult.defra.gov.uk/animal-health-and-welfare/dda_dog-attacks_sentences_survey
(Their emphasis)