The mobile phone operator said a hardware fault in the north west had cut services to "sizeable numbers" of its customers across the UK on Tuesday night (22 January).
A spokeswoman said: "At no point in the past 24 hours did the network go down". She could not give precise numbers of those affected.
"There was a hardware problem in the north west that caused intermittent problems across the network," she said. This, according to Vodafone, had a knock on effect on customers across the UK.
Earlier the company claimed: "Much of the problem occurred overnight". However, angry users told CW360.com that the network was affected from late afternoon.
"I was expecting important business calls after I came out of a meeting at 5pm yesterday. Instead my phone was dead," said one Vodafone user
Another user said: "I thought my phone was on the blink and went scrabbling round the office to borrow one on another network. Vodafone didn't even send me a text message apologising for the problem."
The company apologised to users and said the service was fully restored by Wednesday morning.
Before the network problems Vodafone announced that it had won its 100 millionth customer across 28 countries.