Around 37,000 Sky customers in London have been without a landline or broadband for the last three days after alleged copper thieves cut through BT Openreach fibre-optic cables.
The outage has also affected an unconfirmed number of TalkTalk and BT Broadband customers in one of the most serious network blackouts of its kind in recent years.
The Guardian has reported that suspected thieves accessed a manhole in Brentford on Wednesday night looking for copper cables but only found fibre-optic cables. Nevertheless, the cables were cut, in what BT has described as a "malicious attack".
"Several engineers are on site and working round the clock to reconnect people," a spokesperson for the company said.
BT Openreach engineers have so far managed to restore service in certain areas, with the network expected to be fully operational by 5pm today.
Sky customers have taken to online forums to express their frustration at the situation.
"For me, money won't fix the time I've lost and am still losing every hour. What makes me angry the most is the lack of communication. No update on the status website since 1pm yesterday. Not even an explanation of what has happened," wrote one customer on Sy's help forum.
In a statement Sky said: "(We) are working hard to resolve the outage still affecting 3,000 Sky customers in Chiswick. Please note your broadband speeds may be slower than usual in the recently restored areas while the network resumes full service. We will keep you informed with any updates as soon as we receive them and are sorry for any inconvenience caused."