February 2012 - http://www.hmrc.gov.uk/employers/february.htm

2 February
Forms P46(Car) for the quarter ended 5 January to reach HM Revenue & Customs (HMRC) by this date.

Mid February to Mid March: Expect to receive your notification to file your Employer Annual Return (P35 and P14s) for 2011-12.
19 February
Cheque payments for month ended 5 February should reach your Accounts Office by this date.
22 February
Electronic payments for month ended 5 February should reach HMRC bank account by this date.

Expect your: updated software and instructions from your provider if you use a payroll package.