In July last year, the UK ISPs called for the High Court to launch the review, stating the Act was "rushed through" and had "insufficient scrutiny". The two firms were also concerned that measures to tackle net piracy - including plans to temporarily suspend people from the web - could be in breach of "basic rights and freedoms".
However, the judicial review, which began in March this year, rejected four out of the five claims put forward by the ISPs.
The fifth point, which sees ISPs having to fork out 25 percent of the cost of monitoring web users activities, was upheld by Justice Kenneth Parker and will subsequently be removed from the act.
"We are reviewing this long and complex judgement. Protecting our customers is our number one priority and we will consider our options once we have fully understood the implications for our customers and businesses," BT said.
"This was always about seeking clarity on certain points of law and we have to consider whether this judgment achieves these aims."