From 6 April 2009, Self Assessment customers and Agents can file Self Assessment Returns online for earlier tax years.
The 2007-08 return is the first 'earlier year' return available online and customers will be able to file this return online during the 2009-10 tax year, and for several years after that.
The time limit for HMRC accepting an earlier year tax return is five years and ten months after the end of the tax year to which the return relates. So 31 January 2014 will be the last date on which a 2007-08 tax return will be accepted online.
Over time and as each new tax year begins the number of 'earlier year' returns that customers can file online will increase; although the oldest of these with remain 2007-08.
Further information is available here.