Last month the Premier League added First Row Sports to that list - a Swedish-based site offering video streams to football games from around the world.
The way the system works is that the rights-holders are responsible for identifying which IP addresses are being used and then sending the details to the ISPs.
The court specifically said that ISPs are "wholly reliant" on the rights-holders "accurately identifying" which IPs should be blocked and had "no obligation" to check them themselves.
In addition to Radio Times, several football clubs - including Blackburn Rovers, Reading and Brentford - as well as the Notes from Nature science project and Galaxy Zoo space education site have been affected.
Virgin Media confirmed its subscribers had flagged the issue last week - following discussion about it on the Thinkbroadband forums, external - and added it had taken action to rectify the problem.
"As a responsible ISP we obey court orders when addressed to the company," said a spokesman.
"However, we do not believe the instruction to block this particular IP address meets the criteria of the court order against First Row Sports so we have stopped blocking it and are writing to the Premier League."
Virgin acknowledged this meant that in some cases users might be able to access First Row Sports again.
BT added it was taking similar action.
"Under the terms of the court order to block First Row Sports, it is the Premier League's responsibility to provide BT with IP addresses to block that relate only to First Row Sports," a spokesman said.
"The Premier League is currently looking into whether the IP addresses provided to BT included any IP addresses that related to radiotimes.com. BT has suspended blocking of the IP addresses in question in the meantime".