Customers of the UK's three biggest ISPs were responsible for 65 percent of illegal downloading activity in June this year, says Envisional.

The internet intelligence firm has been tracking music torrent downloads for the past couple of months, and matching the IP addresses to various ISPs. More than 28,000 unique IP addresses were traced in June, 22.6 percent of which used the Carphone Warehouse as their ISP. The next most popular ISP for illegal downloaders was Virgin Media with 21.6 percent, closely followed by BT with 21.2 percent.

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The three ISPs were part of a deal struck last week with the government and the BPI that aims to tackle illegal file sharing. The six ISPs that signed up agreed to issue customers caught downloading illegally with warning letters.

Virgin Media already issued some customers with letters in June, following its own initiative with the BPI. However, the letters don't seem to have had much impact as Envisional's figuresshow that 22.8 percent of July's illegal downloads were undertaken by Virgin Media customers.