Sky News reports that all £100 fixed-penalties will have been sent out by Wednesday (February 20th), adding around £85 million to the department's coffers.
However, this could increase if those affected do not get their tax returns in before the end of April as further penalties are applied if it more than three months late.
An HMRC spokesman told the news provider: "Anyone who hasn't yet sent their 2011-12 tax return to HMRC will have already incurred a £100 late-filing penalty.
"Non-filers have to file online now to avoid further penalties or contact us to ask to be taken out of self-assessment, and provided they meet the criteria, we will take them out of SA and cull any penalties incurred."
Additional £10 daily penalties will be applied, up to a maximum of £900, for returns that are three months late, with further fines following at six and 12 months past the January 31st deadline.
Posted by Thomas Fletcher