Here are official websites. http://www.jlpt.jp/e/ http://www.kanken.or.jp/bjt/english/index.html As far as I know, JLPT is the most popular test among Japanese learners. If you have just started or haven't even started studying Japanese, JLPT level N5 would be your first step. However, these tests are designed mainly for those who want to use Japanese in business and study in Japanese colleges. Otherwise, test is nothing more than test, you know:) Some people are really motivated by taking some test, which is good, but not everyone.

From Wikipedia: The Japanese Language Proficiency Test (日本語能力試験, Nihongo Nōryoku Shiken?), or JLPT, is a standardized criterion-referenced test to evaluate and certify the Japanese language proficiency of non-native speakers. It is held twice a year in East Asia and once a year in other regions.The JLPT now has five levels, with Level N5 the most basic and Level N1 the most difficult. From 1984 to 2009 the test had 4 levels, with Level 4 the most basic and Level 1 the most difficult. But a new level was inserted between 2 and 3, meaning N5 corresponds to the old Level 4. The Japan Foundation estimates that approximately 150 hours of study were necessary to pass the Level 4 exam and 900 hours of study were required to pass the Level 1 test,although the figures may be significantly higher for native English speakers. In 2008, the Japanese government announced a plan under consideration to use the JLPT to screen applicants for long-term and permanent resident visas.The test is held on the first Sunday of July and December each year. You could google it to see when it's held in the UK.

Hi there. You can learn Japanese here at Italki. Go to http://www.italki.com/knowledge/learn-Japanese-English.htm