When we complete a corporation tax return we always suggest that our clients pay their tax bill sooner rather than later as HMRC will pay them a small amount of interest AND it means that they won’t forget to pay. Especially now that HMRC have stopped sending reminders.
HMRC interest rates vary as they are linked to the Bank of England base rate.
If you pay early you will receive interest at base rate minus 1%, so currently 3.25%. (There is a minimum floor of 0.5% if the base rate goes very low). The interest is calculated from the date that you pay until the date you are due to pay.
Yes, you can get better returns on your savings elsewhere, especially as you know when you will need to withdraw it to settle your tax bill.
But, if you forget and pay late, you will pay interest at base rate plus 4%, so currently 8.25%. The interest is calculated from the due date until the date that you actually pay.