Koh Lipe and Koh Adang are a pair of islands far out in the Andaman Sea in the south of Thailand. Although separated by just a kilometre of shallow water, they are worlds apart. Koh Lipe's tropical paradise innocence is being relentlessly violated as bungalow operations feverishly add and upgrade their rooms.

While Koh Lipe is far from completely 'Samui-ed', the process is clearly in motion. But on Koh Adang, a strict ban on all commercial activity ensures that the island is as pristine today as it was 30 years ago.

Both islands are part of the Tarutao National Park, but that alone is hardly enough to prevent over-development. Islands in other national parks, such as Koh Phi Phi and Koh Chang, were irrevocably changed once the government allowed private businesses within park boundaries.

In Tarutao, the government has so far stood firm against private development. So how is that policy being so blatantly flouted on Koh Lipe? In part, because of the people known in English as Sea Gypsies, to themselves as Urak Lawoi, and usually referred to by their Thai name, chao leh - literally, people of the sea.

In 1909, the governor of Satun province settled the chao leh on the islands in order to populate them with Thai nationals in response to the territorial ambitions of the British in nearby Malaysia. The establishment of the Tarutao National Park 63 years later made the chao leh's subsistence fishing and farming illegal. The park's policy is to tolerate the chao leh's 'illegal' activities rather than forcibly remove them.

Entrepreneurs have seized on these chinks in the park's armour to establish bungalow operations on Koh Lipe.

'All illegal,' declares Panapon Chewnserichol, the head ranger for the area - but he is literally powerless to stop them.

Maria Hardy, a British volunteer with the park, says that 'development will evolve on its own on Lipe. But it won't spread'. The park rangers have drawn the line at Koh Adang, where the ban on private development is strictly enforced. So, the situation has settled into an uneasy detente: Koh Lipe is sacrificed to appease commercial interests while Koh Adang is preserved in its pristine state.

Conservationists lament the commercialisation of Koh Lipe and developers weep over lost opportunities on Koh Adang, but for the traveller the situation has evolved into a 'best of both worlds' proposition. Interested in a holiday among seaside cottages and fellow travellers? Koh Lipe. Prefer something very quiet - an island rather than a tourist resort? Koh Adang.

For those not satisfied with just skimming the surface of the ocean, two dive shops on Koh Lipe offer dive trips and certification courses: Sabye Sports at Lipe Resort and Forra Diving at Chao Leh Resort.

Koh Adang - large, isolated and wild - is a great destination for hikers. From its main beach at Laem Son (Pine Cape), the most accessible destination is Jones Salad (Pirate's) Waterfalls, so named because the bandits who plagued the area after World War II used the falls for fresh water.

Although it begins with a short rocky section, most of the two-kilometre trail is quite easy to follow. Those who are quiet and lucky may spot some of the island's wildlife, including crab-eating macaque monkeys and the elusive, 20-cm-tall mouse deer.

Although in the dry season there is not enough water for the falls to be considered spectacular, the spot is still quite lovely. The stream merrily cascades down the granite rock face and the pool makes a perfect spot for a refreshing dip. Hiking - rock climbing, really - upstream reveals an enchanting archipelago of similar small and wonderful waterfalls.

Another trail running from Laem Son in the opposite direction leads to Cha Do Cliff. Perched high on the granite mountains of Adang, the cliff commands a stunning view of Koh Lipe and the surrounding seas. An accessible trail, steep at times, brings you to the first viewpoint. Butterflies are a constant presence, and with a bit of practice and luck, you can spot the many monitor lizards which scurry away at your approach. The first viewpoint is easy to reach, but Cha Do Cliff is an additional 300 metres up a much narrower and steeper trail.

It is, however, well worth it. To the east, nothing but the deep blue of the Andaman Sea; below, Adang's green forests, the white sands of Laem Son and the turquoise channel to Koh Lipe. But Lipe is the real prize.

The entire island lies curved gracefully before you. From the cliff, you see clear across Lipe to the harbour on the far side.

It is a view you can sit and sip for hours. Or at least until sunset, when hawks soar out of Adang's cliffs to be silhouetted against the fiery red sky.

Isolation and remoteness are part of the general appeal of the islands. But they are accessible by ferries, taxis, mini-vans and buses. Whichever route you pick and whichever island you choose, chances are that Koh Adang and Koh Lipe will entice you to return.