Laxmi Mall Singhvi broke the record as India’s longest-serving High Commissioner to London, from 1991 to 1997, at a time of political chaos at home when prime ministers were coming and going and he might at any time have expected the summons home. It was a measure of his diplomatic skills that he survived so long in a job he adored and on which he left a still-remembered mark.

He had his eccentric side, manifested by an obsession with placing busts of Mahatama Gandhi in as many famous buildings as possible in Britain. He even managed to get one in Shakespeare’s house. He was also fond of using his contacts to get universities to give him honorary degrees, of which he had a large collection.

To celebrate 50 years of Indian independence he designed a watch, handed out by the High Commission in London, which contained an engraved message of Indian-British friendship and declaring that the world was one family. He was also fond of handing out an interfaith tie, which he had personally designed, containing symbols of all the main world religions.

Singhvi was one of several Indian high commissioners since independence who were not career diplomats. His long tour was a demonstration of the respect in which he was held across the political spectrum in Delhi, where one newspaper recently described him as “an ambassador of harmony”. He managed to rise to the top as a jurist, constitutional expert, diplomat, writer, historian and scholar of philosophy — and, along the way, to become an MP a couple of times — without making enemies.

His stint in London was the high point of his professional life, when he ceaselessly moved around the upper reaches of British society and became close friends with members of the Royal Family, in particular the Prince of Wales. He was also close to Diana, Princess of Wales, and was responsible for suggesting that she visit the Taj Mahal during her visit to India.

Singhvi brought Jain and Hindu philosophy to nearly everything he tackled, including the law and diplomacy — the latter he described as an enterprise in human relationships. He abhorred the “reckless” consumerism of the West, the environmental impact of which he regarded as a breach of ahimsa, or non-violence. He was an expert on the history and philosophy of Jainism and was involved in editing the Jain Declaration on Nature, a booklet presented to the Duke of Edinburgh, president of the World Wide Fund for Nature, in 1990.

As a senior advocate of the Indian Supreme Court, Singhvi regularly invoked the Dharma Shastras, Hinduism’s ancient codes of laws and ethics, in interpreting constitutional law. His standing as a jurist was recognised by Bangladesh, Nepal and South Africa, all of which sought his advice in drawing up their constitutions. For a time he ran the Indian Law Institute, now recognised as a university offering specialised law courses, and was elected president of the Indian Supreme Court Bar Association several times. He conceived the idea of Law Day, now widely observed by India’s legal profession on November 26 each year.

Singhvi was educated at Allahabad University and Rajasthan University before taking further law degrees at Harvard and Cornell. He was an independent member of the Lok Sabha, the Lower House of Parliament, from 1962 to 1967, but his greatest lasting impact was as a lawyer rather than a politician. He was advocate-general of Rajasthan and was involved in a range of international organisations, including several associated with the United Nations.

He headed the High Level Committee on the Indian diaspora, set up by the Government to increase ties with the 25 million people of Indian origin around the world, many of them prominent businessmen and women who could be encouraged to invest in India. He conceived the idea of an annual Pravasi Bharatiya Divas, an event organised by the Indian Government each January to engage with Indians around the world.

Singhvi established close ties with the 1.5 million people of Indian origin in Britain during his term as High Commissioner and campaigned for dual nationality for Indians living abroad. This led to the establishment of a new category, Persons of Indian Origin, which conferred many privileges of citizenship on expatriates.

Singhvi never displayed any obvious political affiliation but he was seen as a liberal. Friends were astonished, therefore, when he joined the right-wing Hindu nationalist Bharatiya Janata Party after returning to India, for which he became an MP in the Rajya Sabha (Upper House of Parliament) from 1998 to 2004. This was probably an opportunistic move in a failed campaign to become President of India. His contributions to law and public affairs were honoured with a high civilian award, the Padma Bhushan, in 1998.

Two of his books, Freedom on Trial and A Tale of Three Cities, were widely acclaimed, and for nearly a decade he was president of the Authors’ Guild of India. He also wrote poetry and was comfortable in many languages. Some of his books were written in Hindi. One of his last tasks as a lawyer was as a member of a commission of inquiry into the administration of justice in Trinidad and Tobago.

He is survived by his wife Kamla, a son and a daughter.

Laxmi Mall Singhvi, diplomat, jurist and constitutional expert, was born on November 9, 1931. He died of a heart attack on October 13, 2007, aged 76