Looking at the data, the UK rate has been decreasing overtime but has plateaued in recent years and slight fluctuations could be noise. For most of the past 6 decades it has been decreasing steadily but at a decreasing rate.
It also appears different countries count infant mortality differently. Some have cut offs where they consider the live birth to be a still birth for reporting purposes. So it’s not a apples to apples comparison between countries.
https://data.worldbank.org/indicator/SP.DYN.IMRT.IN?end=2022...
On a side note, a friend of mine is a neonatal intensive care doctor. The majority of the infants they care for have issues due to heavy drug use during pregnancy. So at least in my country this has a large impact on infant mortality.