I know that it caught you by surprise last month. These things do creep up on you without notice, so I hope this helps.
Just to let you know, in advance, that there will be a Christmas this year.
It is scheduled for 25th December, and there is a serious risk that the 26th December (known as "Boxing Day") will be a holiday too.
It almost certainly means your accounts staff will be on holiday, your accounts department may even be closed for some time around the end of December, and it is more than likely that the person that signs the cheques will be taking some holiday.
Please take this in to account and get the payment signed off BEFORE this all happens. Otherwise you'll have more late payment penalties next year.
Or better still pay by BACS or Direct Debit, FFS.