There is an automatic 1/3 reduction in sentence for an early guilty plea (as I told you in your original question)
But as the minimum possible sentence is 3 years in prison , the absolute minimum will be 2 years inside.
I personally don't see this as 12 years ,your solicitor says 'up to' 12 years. But I think he is just preparing you for the worst possible outcome. But as I just said, you have to accept that he will get at least 3 years,reduced to 2 for his guilty plea.