You asked
I would like to know the mean average salary in the UK in 2012, and in 2013, and in 2014.
We said
The best source for this information is ONS's Annual Survey of Hours and Earnings (ASHE), which is based on a 1% sample of jobs taken from HM Revenue and Customs' Pay As You Earn (PAYE) records and is the most comprehensive source of earnings information in the United Kingdom. The most recent ASHE data are for April 2014 and the published reference tables are available on the ONS website.
Estimates of mean gross weekly earnings for full-time employees in the UK for April 2012, 2013 and 2014 can be found in Table 4 of the 'ASHE 1997 to 2014 selected estimates' spreadsheet. We also publish a wide range of other earnings estimates, including annual and hourly earnings, in the other reference table zip files on this page.
If you require any further information about ASHE please contact earnings@ons.gov.uk