Michael Brown was sentenced in his absence to seven years in jail in 2008, for fraud including the theft of millions of pounds from Manchester United's former chairman, after he fled to the Caribbean.
He had donated about £2.4 million (2.9 million euros) to the Liberal Democrat Party before the 2005 general election.
The centrist party was not in power at the time, but became the junior partner in a coalition government with the Conservative Party following the 2010 election. Brown, who was arrested in the Dominican Republic in January, was deported to Spain yesterday, a spokesman for Britain's Serious Organised Crime Agency told AFP. British officials will now begin the process of extraditing him under the European Arrest Warrant system, the spokesman said, adding that there would be a hearing in Spain at which Brown could appeal against his extradition.
The alleged fraudster stole nearly £8 million from Man United's ex-chairman Martin Edwards by posing as a bond dealer and claiming connections to royalty.
An Electoral Commission inquiry in 2009 found that Brown was a permitted donor at the time of his donation to the Liberal Democrats, and cleared the party of any wrongdoing.