Yes, you would be seeing it because the UK’s total fertility rate (TFR) has declined from 1.94 TFR in 2010 to 1.55 TFR. TFR is not quite the same as births per woman, it’s more an estimate of the average number of children an average woman would have in her fertile years- the replacement rate TFR is 2.1. Globally, TFR has dropped pretty universally apart from a few outliers such as Nigeria. The U.K. is still in the middle of the range, but we’re seeing ultra low fertility levels (TFR around 1) in places like Japan, South Korea, and increasingly in Europe (e.g Italy and Spain).
Reasons tend to be specific to the particular national context, but often include delays to childbearing due to need to get ‘established’ (employed, stably housed, in a stable relationship- all of which is taking an increasingly large amount of time) plus things which deter larger families such as cost of living, cost of housing, childcare costs. Also big factors include ideals of intensive parenting (as a PP mentioned), sexism, workplaces being unsupportive of parenting, lack of family support etc. Basically, make it hard, unpleasant and expensive for people to have kids and they stop having them or as many….
Sadly, most countries have a ‘fertility gap’ where the stated number of children women want to have (their ‘fertility intention’) remains around 2 or higher, but the number they do actually have is much less. Some places (such as the nordics) have managed to increase fertility but a lot of other places have failed. Mostly because they offer financial incentives (easy) when they really need to do major work on how their societies actually support families (very hard).