Following his retirement from active politics, Oaten published two books, before becoming executive of the International Fur Trade Federation in 2011.
The defeated Conservative former MP Gerry Malone successfully challenged the election on the basis of an established precedent which voided the result where it had been affected by a decision not to count ballot papers which had not been properly stamped.
On 10 January 2006, Oaten declared that he would be a candidate in the leadership election to replace Charles Kennedy, standing on an agenda of making liberalism relevant to the twenty-first century.
On 21 January 2006, Oaten resigned from the Liberal Democrat front bench[7] when it was revealed by the News of the World that he had hired a 23-year-old male prostitute between the summer of 2004 and February 2005.
[17] In 2018, he resigned from the Liberal Democrats after being a member for thirty years[18] but announced that he had rejoined them in September 2019 to "help defeat the new extremes growing in politics".
[19] In the 2023 United Kingdom local elections Oaten stood unsuccessfully for the Liberal Democrats in the Severn Vale Ward of South Gloucestershire Council, receiving 1,435 votes.
Oaten was a member of the Advisory Board of the Liberal Future think tank until it was wound up in 2005, and one of the contributors to The Orange Book: Reclaiming Liberalism in 2004—although he attracted anger from the book's co-authors at its launch event at the Lib Dem Conference in spring 2004 when he refused to answer questions about his own chapter, stating that it had actually been written by his research assistant, and that he had not even read it.
As the party's principal home affairs spokesman, he championed the rights of asylum seekers and civil liberties, condemned calls by then Conservative frontbencher David Davis for the reintroduction of capital punishment and has claimed to want to reunite all the strands of liberalism, and not elevate one above the others.
[citation needed] In February 2010 Channel 4 broadcast a four-part series called Tower Block of Commons in which four MPs lived briefly on different council estates in England.