It put the figure at around $137bn (£66bn) globally.

For users, the slowdown could see a return to the bad old days of dial-up, the report predicts.

Stifling innovation

"It may take more than one attempt to confirm an online purchase or it may take longer to download the latest video from YouTube," the report cited.

But it is the knock-on effect for new services that could be the real problem, report authors think.

"The next Amazon, Google or YouTube might not arise, not from a lack of user demand but because of insufficient infrastructure preventing applications and companies emerging," the report warned.

The demand for bandwidth-intensive applications shows no sign of abating.

Nearly 75% of US internet users watched an average of 158 minutes of online video and viewed more than 8.3bn video streams during May, according to research by measurement firm comScore.

The financial invested required to "bridge the gap" between demand and capacity would range from $42bn (£20bn) to $55bn (£27bn) in the US, Nemertes estimates.

The report is part-funded by the Internet Innovation Alliance (IIA) which campaigns for universal broadband in the US.

"We must take the necessary steps to build out network capacity or potentially face internet gridlock that could wreak havoc on internet services," said Larry Irving, co-chairman of the IIA.