* Storming of temple led to Indira Gandhi's assassination
* Temple is Sikhism's holiest shrine, death toll disputed
* Unplanned release of official documents exposed UK role
* Investigation confirms that but says UK impact limited (Recasts, updates with full statement, report details)
By Andrew Osborn
LONDON, Feb 4 (Reuters) - Britain secretly helped India plan a deadly assault on Sikh separatists holed up in the Golden Temple at Amritsar in 1984, the government said on Tuesday, saying London's influence was limited and there was therefore no need for an apology.
Prime Minister David Cameron ordered a review into the matter last month after the government inadvertently released official papers suggesting that Margaret Thatcher, then prime minister, had sent an officer from the elite SAS special air service to advise India on the raid.
The unplanned release upset British Sikhs, whom Cameron is courting ahead of a national election in 2015, and in India it triggered nationalist criticism of the dynastic ruling Congress party, which faces an uphill struggle to be re-elected in a national vote due by May.
Congress, under then-prime minister Indira Gandhi, was in power at the time of the raid on the Golden Temple, Sikhism's holiest shrine. It was a bloody episode that angered Sikhs around the world; they accused the Indian army of desecration.
The death toll in the attack remains disputed, with Indian authorities putting it in the hundreds and Sikh groups in the thousands.
In a statement to parliament, Foreign Secretary William Hague said an official investigation by Britain's top civil servant had confirmed that an SAS officer had been dispatched to India in 1984 - at the request of the Indian government - to help plan the assault staged in June of that year.
But he said the impact of the officer's influence on events had been limited and that the Indians appear to have disregarded the main elements of his advice.
"The nature of the UK's assistance was purely advisory, limited and provided to the Indian government at an early stage," Hague told parliament. "It had limited impact on the tragic events that unfolded at the temple three months later."
The SAS officer had advised the Indians that a military operation should only be a last resort, Hague said, and that any assault should use the element of surprise and helicopter-borne forces to try to reduce casualties.
Indian forces had not acted upon either piece of advice, he said, and there had been no link between the provision of this advice and British defence sales to India. Nor was there any record of Britain receiving advance notice of the raid.
"It is quite right that the concerns that were raised about UK involvement have been investigated," said Hague. "It is a strength of our democracy that we are always prepared to take an unflinching look at the past."
There had been no "cover-up", he added, saying Britain had sifted through more than 23,000 official documents to establish what had happened.
The storming of the temple, aimed at flushing out Sikh separatists who demanded an independent homeland, led to the assassination of Gandhi in October 1984 when two of her Sikh bodyguards shot her in the garden of her residence.
Cameron visited Amritsar last year to express regret about another bloody incident there - a British colonial-era massacre of unarmed civilians. Politicians from all parties are keen to attract Sikh voters before Britain's general election in 2015. (Additional reporting by William James; Editing by Mark Heinrich)