I can't remember, it was over a decade ago. They probably weren't unrealistic, but given the official line was 'no targets' and there were a lot of training things to attend, it was tricky.
The way it was worked out was the target was calculated at the beginning of a period of time and then not adjusted for staff changes.
So if there were 15 lawyers with targets of 70 units a day for example, and 1 trainee, all fine! If 5 people were off sick/left, the target for the remaining goes up to 105, but if the trainee is included it's 95 average. More pressure = more people off sick and then the target goes up further.
That was just one department I was in though. I worked in a couple of advisory departments which were much more pleasant (and suited me) but I knew it would be at least 2 years before I could move into advisory permanently, and possibly far longer.
If coming at it for pupillage, you spend 6m in Chambers (which is supposed to be your 2nd 6). That was wonderful, though the prohibition on doing court work was deeply frustrating.
I could definitely have made a career in advisory there and enjoyed it, but my heart was in court work. As a PP said, there is a big divide between the two divisions.
In advisory you may be advising government ministers, helping create secondary legislation etc. In litigation, you may be working on large and complex cases, or you may be processing large volumes of court paperwork for failed asylum applications. Some work is far more glamorous, intellectually challenging and pleasant than others. There is a vast range of opportunities. The culture just wasn't for me.