IFLICKED my fins and moved through the glittering water to the bridge of the sunken ship. Violet and scarlet fish moved lazily out of my way. I gripped the rail of the bridge: from a hole in it a silver guppy, the size and general appearance of a safety pin, looked out at me speculatively. The flow of bubbles from my breathing regulator fluttered silently to the surface of the sea, 20 metres above. Down here, virtually nothing had changed since the merchant ship, Thistlegorm, was sunk in 1941 by German planes and settled at the bottom of the Red Sea. She had begun to turn into a coral reef, her decks and body encrusted with strange, waving growths.On the main deck, motorcycles were still chained in rows, the rubber of their tyres turned by half a century in the sea into something thick and hard as rock. I looked at my air gauge: it was time to return to the surface. Out here in the Red Sea, Israeli dive boats are common even though the Sinai peninsular has long reverted to Egyptian control. The scuba-diving industry which the Israelis brought with them after their capture of Sinai in 1967 is still booming, but the Israelis are more cautious nowadays. When we came alongside some Egyptian fishing boats, the small Israeli flag we had been flying was taken down. Not that anybody interferes with the diving industry. Its centre, Sharm el-Sheikh, is a long way from the areas where Islamic fundamentalists operate, and the inhabitants of Sinai are mostly Bedouin who have so far been untouched by religious extremism. Tourism probably brings in more revenue in real terms to the Egyptian Government than anything else except subventions from the United States. The various fundamentalist groups, knowing this, have concentrated much of their effort on attacking tourists in Cairo, in the region around Assyut, and along the Nile. The results have been spectacular. Not in terms of deaths, since no tourist has been killed in Egypt this year, but in the tailing off of the trade. At the Pyramids recently I counted only three buses in the car park where 30 or 40 would once have been jammed in. ''It is finished, my friend, finished,'' said the man in a shop near the attraction. He was trying to sell me the genuine perfume which Queen Nefertiti used on her wedding night with Tutankhamen. ''Until these fundamentalists give up, the tourists will not come back.'' He spent most of the rest of the conversation begging me not to identify him. Since there are about 30 shops around there which sell Queen Nefertiti's genuine perfume, he will probably be safe. But safe from whom? In the old days, it would simply have been from the Egyptian security police, who deal harshly with critics of the Government. Now, it is the fundamentalists as well. Egyptians are wounded and killed by extremists virtually every week, and in the last few months there have been attempts on the lives of President Hosni Mubarak and his Prime Minister, Atef Sedki. The Government responds in kind. Since the beginning of last year, 50 Islamic extremists have been sentenced to death. To anyone who watched the tide of revolution build up in Iran in 1978 and 1979, this has an ominously familiar ring to it. An imperious leader who uses the full force of an unattractive security system to silence dissent. An Islamic opposition which openly courts martyrdom and believes victory is certain. A West (and particularly a US administration) which sees no alternative but to back the Government to the hilt, which, in turn, supports the Islamic opposition's claim the Government has sold out to Western interests. And while there are many differences between Iran in 1978-79 and Egypt today, not all of them are favourable to President Mubarak. For instance, the officer corps in the Shah's army stayed loyal to him right to the end, but there are ominous signs in theEgyptian army the fundamentalists have succeeded in infiltrating the officer corps. Recently, in a trial the official media in Egypt were not allowed to report, three officers were found guilty of plotting to blow up the President at an airstrip near the border with Libya. The situation is not yet urgent. The vast bulk of the army is still loyal to the Government, and just as the murder of President Sadat by Islamic extremists in October 1981 did not result in a collapse of his government, so there is no immediate danger of an Islamic revolution. But things are unquestionably getting more difficult for President Mubarak. The Egyptian Government sometimes blames Iran for it all. But the Iranians, who are Shi'ite Muslims, have little contact with the Sunni fundamentalists of Egypt. The fundamentalists themselves look to private groups in Saudi Arabia for money and to Algeria for tactics. The Government in Algeria now faces a choice between cracking down more savagely than before, or simply allowing itself to be rolled over by the increasingly confident Islamic extremists. Iran has shown how hard it is to combat these things by standard procedures. Yet in the 15 years since the revolution, the Iranian fundamentalist authorities have become corrupt and discredited, and the Islamic republic there has almost run its course and cannot survive much longer. Revolutionary Islamic fundamentalism is an enthusiasm. It burns brightly, but fades fast. It lacks the staying power required for a ruling ideology. On our dive-boat, moored 20 metres above the wreck of the Thistlegorm, my companion, who knew Iran well, sat with me to watch the sun go down over the Egyptian coast. We started discussing where we would like to spend the night of December 31, 1999. She favoured the Pyramids, I the ruins of Persepolis in Iran. ''I'll have a bet with you,'' she said. ''If it's the Pyramids, I'll have to wear a head scarf and we'll be drinking orange juice. If it's Persepolis, I'll be bare-headed and we'll have a bottle of champagne.'' I took the bet; but I wouldn't be surprisedif I lost it.