Internet visits to www.twitter.com have increased by 631% over the last 12 months, with 485% of that growth coming this year. Twitter is more popular with Brits than Americans: last week the site’s share of UK Internet visits was 70% higher its share of visits in America.

Twitter’s size is notoriously difficult to measure, as there are so many access points (mobile phones in particular), so if anything our measurement of internet visits under-estimates platform’s popularity. In her post Heather Hopkins argues that Twitter cannot yet be considered mainstream in the USA, but in the UK it’s getting there. Last week Twitter entered our rankings of the top 50 Social Networking and Forums websites for the first time, and the demographics are also pointing towards more wide-spread adoption. Overr the last 4 weeks, visitors were split 50/50 male/female, while only 15% were from London. 25-34 year olds are still the most over represented age group visiting the site, but 37% of visitors to the site are now 45 and over.

Looking at the Experian Mosaic lifestyle data for Twitter over the same period also paints an interesting picture. The two most over represented types are still both typical early adopters: City Adventurers (High-salaried, twenty-something singles in smart flats in inner urban areas) and Town Gown Transition (Students and academics mix with young professionals in terraces relatively close to universities). However, there are a number of other over-represented types that would imply a more mainstream appeal, in particular Settled Minorities (Young families and singles of varied ethnic decent, in high density, pleasant urban terraces) and White Van Culture (Younger owners, many in good quality ex-council properties, take advantage of local economic opportunities).

Another sign of maturity is that mainstream media organizations are starting to pick up traffic from Twitter. For example, BBC News accounts for 1.46% of the site’s upstream traffic but 1.73% of its downstream traffic - i.e. the Beeb is receiving more traffic from Twitter than it sends there. Other BBC properties in Twitter’s top 20 downstream sites include BBC Sport (1.34%) and the BBC Homepage (0.71%). The BBC Sport feed is very popular: over the last 4 weeks ‘bbc sport’ was the second most popular search term sending traffic to Twitter. As the table below illustrates, it accounted for 5.92% of search traffic to the site, and was joined in the top 10 by two other BBC-related search terms, ‘bbc news’ and ‘bbcsport’.

The other interesting thing that the table above highlights is the growing tail of people search terms sending traffic to Twitter, something that we’ve highlighted before with regards to another social network, Linkedin. This most recent top 10 includes Kevin Rose (founder of Digg, drinker of tea), the blogger Los Havros, and Molly Wood (executive editor of CNET’s Buzz Report).

Tags: access points, age group, buzz, demographics, digg, founders, internet, localization, media, mobile, network, networking, platforms, popularity, social ing, traffic, twitter, uk, urban areas