If you file online, then you have until 31st January 2011 to complete the return for FY 2009/10, but it is best to get it over with as soon as possible I think. It is possible there is an earlier deadline if you want HMRC to collect tax owed via your PAYE code.
If you post a return, the deadline is 31st October 2009. Again, you can send the return much earlier than that it you want to.



