High street footfall was 16.1% lower to 1pm on Thursday than on the same day last week, and down 8.5% on Tuesday, retail analysts Springboard said.
In central London, the drop from last week was more than double the national average, down 34.4%, compared with a fall of 27% on Tuesday.
Compared with pre-pandemic 2019, footfall was down 32.9% across all high streets on Thursday, compared with a drop of 19.6% on Tuesday, and down 52.1% in central London, compared with a fall of 49.2% on Tuesday.
“The key fact is that the impact of the strike today appears to be even greater than the first strike.”
Dee Corsi, chief operating operator at New West End Company, which represents 600 retail, restaurant, hotel and property owners across central London, said: “At a time when optimism has been returning to our high streets and footfall is steadily climbing to pre-pandemic levels, it is truly disappointing to see so many people forced to stay out of London due to this week’s strikes.
“The warm weather should have seen visitors flocking to the West End to enjoy our world-renowned leisure and hospitality offering, but instead trading is being hampered by reduced footfall across the district.
“We hope that a resolution can be found ahead of the weekend to ensure that we can welcome our visitors, bringing domestic spend that is so vital for the recovery of businesses across the capital.”
The strikes come as retailers were relying on their first restriction-free summer since 2019.
Around 40,000 members of the Rail, Maritime and Transport (RMT) union at Network Rail and 13 train operators walked out again on Thursday after talks failed to resolve a bitter row over pay, jobs and conditions.
Just one in five trains are running, and they are mostly restricted to main lines, with around half of the network closed.