Crossing Continents asks what motivates the Red Shirts - the popular movement that staged mass protests in Bangkok which were violently suppressed by the military.
Seeing red in rural Thailand
The recent clashes in Bangkok have revealed a deep political divide in Thailand.
On the one side are the Red-Shirts, supporters of the exiled former prime minister, Thaksin Shinawatra.
On the other are the Yellow-Shirts, who say Thaksin was corrupt and who occupied Thailand's main airports for weeks last year.
As the Red-Shirts prepared to descend on the capital, Lucy Ash was with them in their heartland in the north east of the country.
Kwanchai Praipana says the masses have been politicised
The Reds' rallying point is the romantically named but heavily political community radio station called Udon Lovers, based in the town of Udon Thani.
Its founder, Kwanchai Praipana, says the poor local farmers were turned into political agitators by the repression of the Yellow-Shirts.
"The hand that was made free has been tied up again and we are not able to participate in the system anymore," he says.
Kwanchai takes Lucy to meet a local farmer, who has seen his income soar after he turned to growing mushrooms on the back of cheap credit.
The money was provided under a scheme set up by Thaksin's government - little more than a political bribe according to his opponents.
Red Shirt demonstrators travelled to a rally in Bangkok
In Bangkok she meets the demonstrators on the front line who talk about the sacrifices they have made in order to join the rally.
And she meets Sondi Limthongkul, the founder of the Yellow-Shirts, who accuses the Reds of opposing the monarchy - a serious charge in a nation where King Bhumibol is revered.
"The way they speak on the stage and ... the community radios, they all broadcast together attacking the King."
The Reds deny the charge, saying they support the monarchy - but they believe his closest advisor engineered the coup against Thaksin in 2006.
A week after recording the programme, Sondi Limthongkul narrowly escaped death when he was shot by unknown assailants.
Kwanchai Praipana is in hiding and the Udon Lovers radio station was closed down.
But the genie is out of the bottle - and this new political force will not be easily subdued.
BBC Radio 4's Crossing Continents was broadcast on Thursday, 23 April, 2009 at 1102 BST and is repeated on Monday, 27 April, 2009 at 20:30 BST.
Reporter: Lucy Ash
Producer: John Murphy