Watch sales surged in the final month of 2020, leaving the full year down by just 10% compared to 2019.
The final figure for all sales is likely to be in the region £1.35 billion.
GfK data shows December sales rose by 34%, ending 2020 on -8%.
However, a statistical adjustment every five years added an extra week to the December figure and a 53rd week to the year. GfK says like-for-like comparison would put growth for Great Britain at -10% for the year rather than the -8% shown in the graphs.
The December figure, alone, should be adjusted down by 25%, pegging the monthly increase back to +9%.
Subtracting 2% growth from all the reported figures for the full year means that sales in London dropped by 24% in 2020 and the rest of the country was down 13%.
The luxury end of the market dramatically outperformed the rest of the watch sector, with in-store sales down just 5% for goods priced at over £1,000. The sub-£500 market was down by a quarter.
Online sales rose by 46% with the highest spikes coinciding with the hardest lock down months.