BT and TalkTalk's hopes of seeing the Digital Economy Act overturned have suffered a major - and potentially final - blow in the courts.
The broadband providers have lost a second appeal against the decision not to grant a judicial review of the controversial legislation.
Despite arguing that substantial elements of the act - which seeks to protect rights' holders against online copyright infringement - is incompatible with European Union law, the firms' joint challenge has been thrown out.
BT and TalkTalk's application for judicial review was initially rejected in April 2011, when Judge Justice Parker dismissed four out of the five grounds for review brought by the broadband providers.
However, the firms were given renewed hope of success last October, when Lord Justice Lewison, ruling in the Court of Appeal, said there was a "real prospect of success" for any review of the Digital Economy Act.
A second appeal got underway in January 2012, but has now been firmly rejected, with the court taking the opportunity to clarify a number of points of law.
Speaking to the BBC, a spokesperson for TalkTalk said that while the firm was disappointed with the outcome, the additional clarity provided for all parties was welcome.
"Though we have lost this appeal, we will continue fighting to defend our customers' rights against this ill-judged legislation," the broadband provider stated.
In a similar view, BT said it had sought clarification from the courts that the act is consistent with European law, and legally robust in the UK.
"Now everyone can be confident in how it is implemented," the firm stated. "We will look at the judgment carefully to understand its implications and consider our next steps."
A number of bodies, including the Open Rights Group, are likely to continue campaigning against the legislation, which was enacted in the dying days of the Labour government in April 2010.
The organisation's Peter Bradwell claimed the legislation was drafted using little reliable evidence from industry and does not represent good law.
"This is a policy made on hearsay and assumptions, not proper facts or analysis," he claimed.