HM Revenue and Customs (HMRC) said users of its online service were still experiencing delays filing their tax self-assessment.
HMRC says 204,000 filed their returns on Thursday
The system is recovering from the breakdown on Thursday when the website was out of action for several hours.
HMRC was forced to extend the self-assessment deadline until midnight on Friday.
HMRC says Friday's delays are not as serious and most users should be able to access the site without delays.
"We're very busy at the moment and some people are being delayed". said HMRC spokesperson, Claudine Lashley.
Anyone that fails to file by midnight tonight faces an automatic £100 fine plus interest on any tax due if they missed the original midnight deadline.
But there is an appeals process and HMRC says anyone who feels they have been fined unfairly will be dealt with on a case by case basis.
HMRC estimates that around 34,000 will complete their self-assessments on Friday, that compares with 204,000 returns that were submitted on Thursday.