A study, led by Dave Cooper, professor of management and economic development, has put the cost of the strike saga to the country's GDP at as much as £300m.
The industrial action, carried out by the Rail, Maritime and Transport (RMT) union and now train drivers' union Aslef, has been causing travel disruption on and off for months.
The research explored the impact on productivity of the strikes and calculated the total economic costs to the thousands of commuters who have been delayed, missed work or had to stay at home as a result of the action.
Professor Cooper said: "The findings put the impact on the economy at about £11m for every day and, if the next scheduled strike days go ahead, the total would be brought to just under £396m."
He added that this could actually be higher still, as the research didn't account for other potential impacts like loss of sales and staff morale.
Read more: Christmas strikes: Why all the walkouts?
“The strikes in December could cost between £47m and £55m and will impact London’s retail and service economy at a critical time of the year - small businesses will be unable to absorb these additional costs and individuals are losing their jobs as a result," Cooper said.
It comes as passengers suffer the second day of a 48-hour strike by the RMT over proposed changes to their roles. There's also an ongoing overtime ban imposed by Aslef.
The RMT's general secretary has said the government could deliver a Christmas truce, but the Department for Transport has said the union's comments over recent contract agreements where conductors were kept, were misleading.
- Saturday 31 December to Monday 2 January (RMT conductors’ strike)
- Monday 9 to Saturday 14 January (Aslef & RMT drivers’ strike)