Internet TV subscriptions worldwide doubled in 2007, according to new research by Informa.

The number of IPTV subscribers has now hit 12.3 million worldwide, driven by a boom in western Europe where some broadband suppliers offered the service for free.

A report published by research firm Informa Telecoms & Media revealed that western Europe now accounts for 57% of global IPTV subscribers, with the boom led by uptake in France.

Informa said that France Telecom, Iliad's Free, Neuf and Telecom Italia's Alice had attracted more than five million IPTV subscribers between them in France by bundling IPTV services free with their broadband packages.

China now has about one million IPTV subscribers and Hong Kong already had one million in September, making it the world's most mature IPTV market.

The US added more than one million IPTV customers in 2007, largely thanks to fiber-to-the-home rollouts by Verizon and AT&T, says Reuters.

In the UK, BT more than doubled its subscriber numbers to reach more than 100,000.

But the report questions whether ISPs will continue to offer IPTV services free or whether they will opt to start charging for what could be a lucrative revenue source for them.

The fees from IPTV services could, for example, counter the declining sales of fixed-line connections for voice calls.

The report says: "It will be interesting to note their approach to IPTV in the future: whether it is used to increase customer loyalty or whether it is a genuine money-making stand-alone service".