A free metropolitan Wi-Fi network has been launched in London, continuing the gradual trend toward free public wireless Internet access in Europe and the United States.

The group behind Free-hotspot.com, which serves as a resource for those looking for Wi-Fi hot spots, and the Wi-Fi network infrastructure firm MeshHopper have joined forces to offer free Wi-Fi access to businesses and the public along a 13.6-mile stretch of the River Thames.

MeshHopper’s fee-based Thames Wi-Fi network, which went fully commercial last year, covers the same stretch of the river, from Millbank in central London to Greenwich in southeast London.

The free network, which is being marketed at “Online-4-free.com,” gives users free access if they agree to view an advertisement of 15 to 30 seconds in length every 15 minutes. If users don’t want to view the ads, they are charged one of a range of fees, including $6 (2.95 pounds) per hour or $20 (9.95 pounds) a month.