Thanks for the question. There are several ways this could be interpreted and answered - and some important limitations with the data to consider, writes data journalist Joely Santa Cruz.
The Office for National Statistics releases immigration data as a rolling annual average, which means it doesn't align perfectly with government terms. So, the figures I'll be using here are rough weighted averages.
Liz Truss wasn't even prime minister for long enough to coincide with an ONS immigration data release!
There have also been some major changes to the way these figures have been collected over the years. Most recently, during the pandemic, the ONS stopped using passenger surveys to estimate migrant flows and switched to using administrative data, including entry visas. The methodology is currently designated "under development", and the latest figures are still provisional.
So we should take these figures with a pinch of salt, especially the more recent numbers. If at the next census we find out that a decade's worth of immigration estimates were quite significantly out, it wouldn't be the first time this has happened.
Still, it should give us a good idea of trends, and as the spikes in the chart below suggest, there are some clear frontrunners. The blue (Conservative) and red (Labour) background colours indicate the party in power, with prime ministers and major events highlighted.
I have used net migration - the difference between people arriving (immigration) and leaving (emigration) - as this is the headline figure people typically refer to on immigration. It also gives a fuller picture by accounting for those who have left the country, such as students and workers at the end of their visas.
Any figure above zero means more people have moved to the country than out of it in that year.
Bearing these major caveats in mind, here are the top contenders:
Net migration overall, and in terms of absolute change from the previous government, was highest during Rishi Sunak鈥檚 premiership, at around 733,000 people a year on average.
This was an increase of around 332,000 annually, or 83%, from the average under his predecessor, Boris Johnson (ignoring Liz Truss here for simplicity).
The second-biggest increase in absolute terms was under Boris Johnson, with a rise of 169,000, or 73%, from the level of net migration throughout Theresa May's term. Had his leadership not coincided with COVID lockdowns and restrictions on travel, this figure may have been higher.
There were many reasons underlying the overall rise under both prime ministers: notably a big increase in immigration from outside the EU for work and study under the new post-Brexit immigration system, as well as an increase in migrants on humanitarian routes from places like Ukraine and Hong Kong.
But in terms of change relative to the starting point, it could be argued that the increase under Tony Blair's Labour government was greater.
Although the increase of around 154,000 was smaller in absolute terms than the increase under Sunak, it represents a larger percentage rise of 390% from his predecessor, John Major. This is greater than the 83% increase for Sunak and also exceeds the 215% increase between Theresa May and Rishi Sunak鈥檚 governments.
Again, there were many factors at play here, with the expansion of the EU a major, but not the only, reason.
Joely
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