By Sarah Toyne BBC News Online personal finance reporter

It is quite encouraging really because we have got so many people trying to file online

Inland Revenue spokeswoman

The system cannot cope with demand and is blocking people from filing online at certain times of the day.

The Revenue has now advised people not to use the self assessment internet service between 7pm and 11pm.

The news of another computer problem comes within the same week as an announcement by the Revenue that a computer enhancement meant it could extend the tax deadline for some people filing online

Revenue's response

The Revenue said people were "working around the clock" to fix the problem.

A spokesman said there had been such an increase in demand that the capacity was insufficient to process so many returns at one time.

"There are so many people that it is a bit sluggish at the moment.

"It is quite encouraging really because we have got so many people trying to file online."

The Revenue has published an apology online.

"Due to an unprecedented increase in the number of customers wanting to use SA Online, at certain times some are currently unable to gain access.

"We are working around the clock to remedy this and apologise for any inconvenience caused to customers affected."

On Friday morning this notice was no longer there.

String of gaffes

This is the latest embarrassment for the Revenue's e-filing service.

Earlier in the year the online filing system was hit by a security scare.

Some users were able to access other people's details online.

Chas Roy-Chowdhury of the Association of Chartered Certified Accountants (ACCA), said: "There should be a root and branch investigation about what is going wrong with the Revenue's computer systems.

"It doesn't do anything for people confidence if they are trying to file online."

Earlier in the week, the Revenue announced that it had made a computer "enhancement" for PAYE taxpayers, and so it could extend the deadline for a portion of e-filers to 30 December 2002.

People who owe no more than £2,000 for the year to 5 April 2002 can have their tax collected through next year's PAYE coding, and have an additional three months to get their internet returns in.

The 30 September deadline still applies for people who file paper returns.

So far this year 113,000 out of about 9 million returns have been filed online, an increase on last year's 75,000.

One advantage of filing online is that the system will automatically calculate their tax for them.