There are four important deadlines for employers in April and May.
April 19
Outstanding PAYE tax and Class 1 NICs – postal payments must reach your HMRC Accounts Office.
April 22
Outstanding PAYE tax and Class 1 NIC – cleared electronic payments reach HMRC bank account.
As 22nd April 2012 is a Sunday, the payment will need to clear into the HMRC account by Friday 20th unless you are able to arrange a Faster Payment to clear on or by the 22nd. You should check with your bank in good time to see if you are able to use Faster Payments; what single transaction/daily limits affect the amount payable, and when you need to arrange payment for it to clear by the 22nd.
May 19
File your Employer Annual Return (P35 and P14s). If you are exempt from the requirement to file your Employer Annual return online your paper return must reach HMRC Customer Operations Employer Office by 19 May.
May 31
Give each relevant employee a form P60.
Further information about year end routines for PAYE can be found on the HMRC webpage: PAYE Year End Routines