The UK is to introduce new measures that will see internet service providers (ISPs) block pornography by default, where consumers will soon have to opt-in if they wish to view pornographic content.

Prime Minister David Cameron is expected to say that free access to online pornography is "corroding childhood", but has also told BBC Radio 4's Woman's Hour that he expects a "row" with ISPs.

ISPs argue that blocking content is unworkable and that as a matter of 'freedom of speech', customers should be able to search whatever terms they wish into websites such as Google or Bing.

Cameron is expected to say that filters blocking content will be automatically selected for all new customers, which will then have the option to switch them off. However, millions of existing customers will be contacted by their ISPs and told they must decide whether to activate 'family friendly filters' to restrict adult material.

Customers who do not click on either option - to accept or decline the filter - will have content blocked by default, according to the BBC.

Search engines will also be given until October to introduce further measures to block illegal content. For example, Cameron will also introduce new measures that classify pornography depicting rape as illegal.

Further to this a secure database of banned child porn images gathered by police across the country will be used to trace illegal content and the paedophiles viewing it.

David Cameron will say: "I want to talk about the internet, the impact it is having on the innocence of our children, how online pornography is corroding childhood.

"And how, in the darkest corners of the internet, there are things going on that are a direct danger to our children, and must be stamped out.

"I'm not making this speech because I want to moralise or scaremonger, but because I feel profoundly as a politician, and as a father, that the time for action has come. This is quite simply about how we protect our children and their innocence."