As Britain's Queen Elizabeth and Thailand's King Bhumibol Adulyadej sit down to a private dinner in the old Thai capital of Ayudhya tonight they may appear to be at opposite ends of the royal spectrum - the first fighting disillusionment with the monarchy, the other revered. In fact there is much they could talk about. For the Queen - who arrived in Thailand yesterday on a five-day state visit - and King Bhumibol now face remarkably similar problems with their families and the royal succession. King Bhumibol, born a year after the Queen in 1927, has reigned for 50 years and is the world's longest reigning monarch. The Queen has been on the throne for 44 years. The Thai king has learnt to become a quasi-divine force for unity in a country that has seen 17 coups, 15 constitutions and 21 prime ministers during his reign. The Queen has overseen Britain's struggle to cope with the loss of its empire and has worked hard to keep the 53-member Commonwealth healthy. After decades of worthy service, they command the respect of their subjects. However, neither of their heirs are held in such high esteem. The Thai king and British queen have also had to deal with their children's difficulties in coping with the flattery, busy idleness and public scrutiny of life as a royal. They each have four children. Thailand's Crown Prince Maha Vajiralongkorn, like Britain's Prince Charles, is in his 40s and unpopular. He has also controversially abandoned a wife for a longtime mistress. While Prince Charles' break with Princess Diana received global publicity, the Crown Prince's marital problems have been treated much more circumspectly, given that insulting the royal family is a serious offence in Thailand. But behind closed doors, many Thais whispered their alarm when the prince dumped his first, royal-born wife, Princess Soamsawali, and a daughter, Princess Bhajara Kitiyabha, for a sexy former actress who became Princess Sujarinee when they married two years ago. Now the Crown Prince's second marriage has floundered. A notice on the wall of the prince's house in northern Bangkok earlier this year banished Princess Sujarinee and her alleged lover, 60-year-old former royal aide Air Chief Marshal Anand Rodsamkhan, from Thailand for life. Alongside photographs of the offending couple the notice accused them of 'adultery' and 'offending an institution'. It read: 'These two people have been declared persona non grata and expelled from the palace. If anyone sees them they must be shunned . . . The institution and Thai Government does not want him to return to Thailand.' As with Prince Charles and Princess Diana's acrimonious split, observers in Thailand say the public nature of the dispute reflects the bitterness involved in the couple's breakup. Princess Sujarinee, who now lives in England, has told the British police that the prince snatched their youngest child, the only daughter, Princess Siriwanwaree Mahidol. No formal complaint was made so the British police took no action. Both British and Thai heirs have aired their frustrations in an unprecedented manner in the media. In 1994, Prince Charles gave an interview on British television in which he spoke about his marital problems and his views on his role in an attempt to improve his image. Four years ago the Crown Prince lashed out at rumours surrounding his private life in a talk to selected Thai journalists. 'I don't understand why whenever anything goes wrong it is always linked to me,' he complained. 'The rumours even say I act as a powerful jao poh [gangster], providing protection for sleazy businesses to operate beyond regular hours . . . I'm also accused of rigging the lottery,' he said. He condemned unnamed individuals for using his name to 'threaten others or abuse their authority'. Prince Vajiralongkorn is understood to have the support of Thailand's Queen Sirikit whose place, like Queen Elizabeth's consort Prince Philip, is to remain on the royal sidelines. But there is no automatic right of succession in the Thai monarchy. The current constitution stipulates that the privy council makes its choice after taking into account the known wishes of the past monarch. Many Thais would prefer the 38-year-old unmarried middle daughter, Princess Sirindhorn, to succeed to the throne. The oldest daughter, Princess Ubol Ratana, is out of the running after marrying an American. Princess Sirindhorn is in some ways the equivalent of Britain's hardworking Princess Anne. For the unostentatious princess, like no-nonsense Anne, works hard and appears to believe in old-fashioned notions of public service. The constitution was amended in the mid-1970s to allow a woman to become monarch. The current Thai constitutional monarchy was modelled on the British system of giving the monarch grand but limited powers except 'the right to be consulted, the right to encourage, the right to warn', as the British economist and constitutional expert Walter Bagehot explained in 1867. But unlike Britain's much maligned institution, the Thai king is still revered by his people. Thai film-goers stand for the screening of his picture and the national anthem in cinemas, and portraits of the king are widely on display. Thailand's constitutional monarchy was only 14 years old when King Bhumibol ascended to the throne after 700 years of absolute monarchy. And down the ensuing decades he has acquired what the respected former prime minister Anand Panyarachun recently called 'reserve powers'. The king has built up his subjects' esteem through his tireless work on behalf of the nation. He admonishes or advises officials and ordinary citizens alike and promotes a host of different projects to help his people, especially poor rural farmers. This was spectacularly shown in May 1992 when a quiet 10-minute lecture electrified the nation and abruptly stopped a bloody confrontation between pro-democracy protesters and an army junta. Viewers on all television channels saw the prime minister General Suchinda Kraprayoon and his principal opponent Chamlong Srimuang prostrate themselves before the king, before being told off like errant children. Without those hard-earned 'reserve powers', many Thais worry that a key force for stability will be missing when King Bhumibol leaves the scene. Queen Elizabeth has similarly dedicated herself to her role. But she has seen the royal house thrown into disarray by her children and their relationships - all of which have been subject to intense scrutiny by the media. In 1989, Queen Elizabeth said: 'Like all the best families we have our share of eccentricities, of impetuous and wayward youngsters and of family disagreements.' Five years later all three of her married children had separated in a blaze of publicity. The Thai king is in a good position to commiserate with her about family problems although he does not have to contend with the amount of dirt-digging by the paparazzi that the Queen faces. The media could get into serious trouble in Thailand for publishing royal scandals. Besides the Crown Prince's troubled relationships, the king's youngest daughter Princess Chulabhorn recently admitted in the best-selling Thai Rath newspaper that her marriage to a former air force officer had effectively finished several months ago. Princess Chulabhorn now spends her time recording syrupy songs of love and heartbreak. As for the future, while the Queen may worry that the behaviour of her children may strengthen calls for the abolition of the monarchy in Britain, the Thai king has a prophecy to contend with. There may be no movement in Thailand to scrap a monarchy that plays a vital unifying role, frowns on extreme political behaviour and is probably also an important psychological comfort for many, but all Thais are aware of a forecast made at the beginning of the current Chakri dynasty that there will be only nine kings in the dynasty. The present king is the ninth. Yes, there should be plenty to talk about over dinner tonight.