It had been widely reported that the change would be put in place next Monday.
Barriers will be introduced so under 18s won't be able to see pornographic content and adults would have to submit ID documents before being granted access online.
However, the delay has disappointed campaigners for child safety.
A spokesperson from the Department for Digital, Culture, Media and Sport said: "This work is a world-leading step forward to protect our children from adult content, which is currently far too easy to access online.
"We are taking the time to get the implementation of this policy right and to ensure it is effective, and we will announce a commencement date shortly."
James Mildred, spokesperson for the Christian lobby group CARE said the UK government are doing more than anyone else.
He said: "We have to give credit where credit's due - the government have been very bold in bringing age verification and we're going to be one of the first countries to introduce this scheme.
"Other countries are looking at what we are going to do very closely to see if they can learn from it.
"The government's timetable has slipped repeatedly and this is very, very concerning...we obviously want age verification to be introduced as quickly as possible."
He appealed to the goverment to not put it off further: "A child is still a child until they become an adult, not when they reach for their smartphone. And at the moment, children are accessing pornographic content with alarming regularity, and they're doing it accidentally as well."
Susie Flashman-Jarvis, a former model, Christian and now life coach told Premier: "I am so disappointed, I had quite a lot of hope that they were going to do something to change things. So to hear that they've delayed it when we know that children access pornography for the first time when they're, like, in primary school - so we're not talking just about under age 14, 15-year-olds - we're talking about young children who haven't even accessed secondary education.
"So I think we have responsibility and quite frankly, they need to pull their finger out and do something about it because we're losing generations to ruined sex lives in their future lives, ruined marriages, ruined relationships. So I think, yeah, I'm very disappointed actually, and I hope they've got a good reason for it."
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