More misery for BT broadband users after new power cut
BT and Plusnet users were unable to access some websites again, after problems with the service yesterday.
The firm said the fault stemmed from Telehouse North, an exchange in London's Docklands.
Telehouse North confirmed that its network had been affected by a tripped circuit breaker but that engineers were now on site.
BT said that connectivity returned to normal by 13:45 BST, though some larger businesses may still have problems.
There were reports of other organisations experiencing connectivity trouble, including HMRC.
On Wednesday, many customers found they were unable to visit certain websites and access some internet banking services.
Those difficulties were blamed on a separate power cut at the Equinix Telecity Harbour Exchange.
A spokesman for Linx - a partner of Equinix - confirmed that its systems were unaffected today.
Telehouse North said the tripped circuit breaker at its facility had impacted "a specific and limited group of customers".
"The problem has been investigated and the solution identified," a spokesman added. "Our engineers are working with our customers on the resolution right now."
Other organisations suffered connectivity problems.
HMRC tweeted a statement saying that customers might have difficulties accessing their systems due to "a national IT supplier having UK-wide broadband infrastructure problems".
And AIB said "technical issues" had affected internet, tablet and mobile banking.
However, it was not clear that these faults were caused by the Telehouse North power failure.
In today's statement, BT said that the latest power failure was "substantial" but had affected "less than five percent" of customers' internet usage.
"BT took immediate action to minimise these issues by redirecting traffic," it said.
Security expert Alan Woodward at the University of Surrey told the BBC the issues were a "concern".
"If this level of disruption can be caused by a power problem on one floor of one building housing part of the infrastructure in the UK, you really have to ask how resilient is this piece of critical national infrastructure," he said.
"Security doesn't just mean protecting against attackers, it means reliability too."