There is a whole separate magazine in the February edition dedicated to cars.
Yes, nearly half of the available city cars have automatically been classed by Which? as "Don't Buy" because of their NCAP star rating.
That is, not for the first time, a complete and utter over-reaction by Which ?
As is pointed out here, Euro NCAP assess cars and awards their scores on the following basis
en.wikipedia.org
5 star safety: Overall excellent performance in crash protection and well equipped with comprehensive and robust crash avoidance technology
4 star safety: Overall good performance in crash protection and all round; additional crash avoidance technology may be present
3 star safety: At least average occupant protection but not always equipped with the latest crash avoidance features
2 star safety: Nominal crash protection but lacking crash avoidance technology
1 star safety: Marginal crash protection and little in the way of crash avoidance technology
0 star safety: Meeting type-approval standards so can legally be sold but lacking critical modern safety technology
And cars safety ratings can and do change as the Euro NCAP ratings have changed over time.
So, for example, the Citroen C1 in 2014 got a 4 star rating
https://en.wikipedia.org/wiki/Citroën_C1#Safety_2 yet would be unlikely to secure such a rating now.