Inland Revenue staff say that self-assessment computer systems, built by US services company EDS, have coped better than last year with the last-minute rush to meet the 31 January deadline.
However, staff say that problems with access to the system in the morning, when most staff log on, remain.
When self-assessment forms are submitted they are scanned into the system, which records the date and the identity of the sender. Information written on the forms is still entered onto the system manually.
One of the main challenges for the system is coping with hundreds of thousands of last-minute returns.
Revenue officials at the Public and Commercial Services Union said this time last year they were inundated with complaints about the system from staff around the UK. But this week a union spokesman reported, "It is all quiet this year."
However, he added that the systems continue to lock out many staff between 9am and 11am. This is understood to be because software controls the number of staff who can log in, to prevent crashes.