The British intelligence services may have just had one of their best-kept secrets blown: their role in the abduction and assassination of Patrice Lumumba, Congo’s first democratically elected prime minister whose Pan-African nationalism and pro-Moscow leanings alarmed the West.

For more than 50 years, rumours have swirled over allegations of British involvement in Lumumba’s brutal murder in 1961, but nothing has ever been proved — leaving the CIA and its Belgian peers alone to take the rap for what a Belgian writer has described as “the most important assassination of the 20th century.” Now, in a dramatic revelation, a senior British politician has claimed that he got it from the horse’s mouth that it was MI6 that “did” it.

In a little noticed letter to the editor in the latest issue of the London Review of Books (LRB), Lord David Edward Lea responded to the claim in a new book on British intelligence, Empire of Secrets: British intelligence, the Cold War and the Twilight of Empire by Calder Walton, that the jury is still out on Britain’s role in Lumumba’s death. “The question remains whether British plots to assassinate Lumumba … ever amounted to anything. At present, we do not know,” writes Walton.

Lord Lea retorted: “Actually, in this particular case, I can report that we do. It so happens that I was having a cup of tea with Daphne Park… She had been consul and first secretary in Leopoldville, now Kinshasa, from 1959 to 1961, which in practice (this was subsequently acknowledged) meant head of MI6 there. I mentioned the uproar surrounding Lumumba’s abduction and murder, and recalled the theory that MI6 might have had something to do with it. ‘We did,’ she replied, ‘I organised it.’”

According to Lord Lea, she contended that if the West had not intervened, Lumumba would have handed over Congo’s — now called Democratic Republic of Congo — rich mineral deposits to the Russians. When contacted by The Hindu, Lord Lea confirmed the contents of his letter to the LRB and that the conversation over tea took place a few months before Ms. Park died in 2010. “That’s the conversation I had with her and that’s what she told me. I have nothing more to add,” he said when asked if he had any other independent confirmation of Ms. Park’s claim.

Ms. Park was a career intelligence officer who served in Kinshasa (then Leopoldville) between 1959 and 1961. On retirement, she was made a Life peer as Baroness Park of Monmouth. Her fellow peers in the House of Lords referred to her as a spokesperson for the Secret Intelligence Service. She was also briefly head of Somerville College, Oxford University.

There has been no comment from MI6 on Lord Lea’s revelation. “We don’t comment on intelligence matters,” an official said.

Lumumba, hailed as “the hero of Congolese independence” from Belgium in 1960, was shot dead on January 17, 1961 after being toppled in a US-Belgian backed military coup barely two months after being in office.

Lumumba had been sheltered by Rajeshwar Dayal — the Indian diplomat who was the UN Secretary General’s representative in the Congo — for several days but was captured and killed soon after he chose to leave the compound. “This heinous crime was a culmination of two inter-related assassination plots by American and Belgian governments, which used Congolese accomplices and a Belgian execution squad to carry out the deed,” wrote Georges Nzongola-Ntalaja, a specialist on African and Afro-American studies and author of The Congo from Leopold to Kabila: A People's History.

Declassified American documents from the time have established Washington’s role in covert assassination plots — the most famous being a CIA plot to poison Lumumba’s toothbrush by smuggling poisoned toothpaste into his bathroom.

“The toothpaste never made it into Lumumba’s bathroom. I threw it in the Congo River,” Larry Devlin, the CIA station chief in Leopoldville, later said.

Not much is publicly known about UK role. But, in 2000, the BBC reported that in the autumn of 1960 — three months before Lumumba was murdered — an MI5 operative in the British embassy in Leopoldville suggested “Lumumba’s removal from the scene by killing him.”