More and more people are switching to filing tax returns online, HM Revenue and Customs says, as the deadline for filing paper returns arrives.The number of people filing online has risen already this year, up a third on the same stage last year.A spokesman said that bringing forward the deadline for paper returns had provided the "impetus" for people to switch to internet filing.The new deadline to submit paper tax returns is Friday.People who miss the deadline will be fined £100, although forms delivered by hand will be accepted at Revenue offices before they open on Tuesday, 4 November. However, not all offices have letterboxes.This year, the self-assessment system is undergoing its biggest change since it was first introduced in 1996, with the forms being significantly revamped.There is now only one deadline for paper returns, which has been brought forward from the end of January. People filing online will be able to keep to the old deadline of 31 January 2009.CampaignAn advertising campaign, alerting people to this change, currently features the former BBC newsreader Moira Stuart.Some 1.8 million people have already submitted their income tax details online, a third more than by the same period last year.A spokesman for the Revenue said that they would usually expect two million people to have filed online by the end of December, but this year they were expecting to hit that mark in the next couple of weeks.There are about nine million people in the self-assessment system.