Mr Harding, 43, was kept in a Moscow airport cell for 45 minutes having just landed back in Russia from London.
He had been in Britain for the previous two months writing about the US diplomatic cables published by WikiLeaks.
In his coverage he reported claims that Russia under Vladimir Putin had become a “virtual mafia state”.
He was sent back to Britain on the first available flight having had his visa annulled and his passport handed back to him only when he was seated on the aircraft.
Mr Harding, who worked at The Argus from 1991 to 1993 and lived in Montpelier Road, Brighton, is the co-author of a forthcoming book about WikiLeaks.
It is due to be published next month.
He is believed to be the first staff journalist to be ejected from Russia since Angus Roxburgh, of The Sunday Times, in 1989.
Mr Roxburgh was sent home after Britain asked 11 Russian spies to leave London.
The British government intervened to prevent Mr Harding from being expelled last year and The Guardian quotes him as saying: “I’m sad to leave under these circumstances.
“But I do not think journalists can accept self-censorship.”
A number of journalists have been killed in Russia after falling foul of the government, with Brighton journalist and academic Roy Greenslade regularly recording their plight.
One example – with links to others – can be seen by clicking here.
The Foreign Secretary William Hague has already contacted his Russian counterpart to ask for an explanation of Mr Harding’s expulsion.
And MPs have called for an invitation to the Russian Foreign Minister to visit London to be withdrawn until the Russian government gave a proper explanation for the incident.
LIKE WHAT WE DO? HELP US TO DO MORE OF IT BY DONATING HERE.