Norman Parker with a FARC commandant, Alfonso

Having persuaded a magazine to fund the trip, off I went to Bogota.

From the Colombian capital, I flew north to meet Edgar in the jungle town of Barrancabermeja.

Fighting in the area

From here on, all travelling would be done by motorised canoe.

Edgar warned nothing was guaranteed, as all parties to the civil war - the Colombian army, the left-wing rebel groups FARC and ELN, and the right-wing paramilitaries - were fighting in the area.

At first glance the vast mountainous interior of Colombia seems hardly worth fighting over. But the land is fertile and the crop of choice, coca leaf, is highly profitable.

Norman Parker with one of the thousands of coca bushes

A two-hour trip up the Magdalena river took us to El Bagre, a FARC-controlled village.

We sat about for a day until going on to the ELN-controlled San Lorenzo.

On the way we passed through an eerie, deserted village called Cuatro Bocas, where 10 villagers had been massacred a week earlier by the paramilitaries.

We had seen abundant evidence that both FARC and ELN taxed the cocaine trade, but the ELN denied any involvement.

'High degree of collusion'

On the morning of the third day, we set out for the cocina, up the very road which 600 paramilitaries had travelled only hours earlier to attack the ELN.

We passed through the same army-controlled checkpoint on the outskirts of San Pablo, which pointed to a high degree of collusion and co-operation between the Colombian military and the paramilitary irregulars.

A jolting, three-hour drive took us to the cocina, or rather to the farm where it was located.

The farmer was dirt poor, living in wood and straw huts.

A worker uses a garden strimmer to cut up the coca leaf

Workers pour cement powder onto the coca leaf

Everything he needed had to be brought in by canoe.

The cocina itself was a long shed without walls, its roof held up by six beams.

On the floor beneath was spread out two large, black plastic sheets.

On the first, a worker was chopping a pile of coca leaves into smaller pieces with a strimmer.

On the second, more workers trod cement powder into the chopped leaves and mixed them with petrol in large black drums. The resulting coca base, a viscous white fluid, is then drained off and treated.

This cocina turned out 15 kilos of coca base per week.

It is bought up by middlemen from Cali and Medellin, who distill it into crystal form before shipping it abroad.

Back at our hotel in San Pablo, four plain-clothed paramilitaries questioned us about our activities.

As soon as they left we got on the next boat to Barranca.

'Few scruples about drugs'

So who did we see benefiting from the cocaine trade? Everyone.

Base cocaine - in large crystal form - is sold to middlemen

The guerrillas, constantly under attack from the Colombian army and the paramilitaries, tax the trade to fund their activities.

The paramilitaries also play a major role in collecting and distributing the coca base, yet they work closely with the Colombian military.

This is deeply ironic considering that the US is currently giving the Colombian Government $1.6bn under Plan Colombia, which is designed to halt the cocaine trade.

Norman Parker's latest book, Life After Life, is available from bookshops