In October the electronic payment deadline of the 22nd (for PAYE) falls on a Sunday.

To make sure your payment for that month reaches HMRC on time, you need to have cleared funds in HMRC's account by the 20th unless you are able to arrange a Faster Payment to clear on the payment deadline. 

If your payment is late you may be charged interest and / or a late payment penalty. So that you know what date to initiate your payment and make sure HMRC receive it on time, you may need to speak to your bank / building society well in advance of making your payment to check cut off times.