It would be an interesting set of data, but unfortunately it seems that the design of the migration surveys will fail to pick up this specific reason for returning to the UK. From a public finance, healthcare and growth perspective, it is clearly of interest if the UK nationals returning to the UK are retired / not economically active, and the UK nationals emigrating are younger and were previously part of the labour force.
The numbers in any given year are relatively small but would become significant when repeated over a prolonged period.
For the latest data, the 88k Brits returning were part of the overall inward migration of 1.163mn, and 92k Brits left the country as part of the overall outward migration of 557k, which obviously gives us the 606k net immigration figure. As such the net change in the overall numbers of British citizens was just 4k, essentially nil from a statistical perspective, but the 180k gross change could be significant if the people leaving and returning had very different characteristics.
As always with these type of data, the gross figures are more informative than the net. It would be ironic if migration trends are also contributing to the decline in the economic activity levels of the UK born population, which in turn requires further immigration to support the economy.