India's answer to the British Gas "tell Sid" campaign – an unprecedented advertising blitz directed at virgin stock market investors – pulled in a record five million retail subscribers to the £15 billion flotation of Reliance Power.

"It is the largest subscription of any IPO anywhere," Anil Ambani, the RPower chairman, said. The industrialist, set to beat his estranged brother, Mukesh, to become India's richest man through the country's largest IPO, claims that RPower will have the biggest shareholder base in the world when it lists in Bombay next month.

Launched in the teeth of a global market malaise, the float – of a power company yet to produce a single watt of power – raised about £1.5 billion. Subscriptions worth nearly £100 billion – the market value of Google – were booked as the Indian public jostled with the likes of George Soros's Quantum Fund for a slice of a business that aims to plug the nation's shortfall in electricity production by building new plants.

Behind the fervour was a sweeping £4 million ad campaign – massive in Indian terms – designed to entice the country's "urban youth" and young women in particular.

Since the New Year, visitors to Mr Ambani's Adlabs cinemas and listeners to BIG FM, his radio station, have been bombarded with the tagline "Power on. India on" – as have callers put on hold while dialling users of Reliance Mobile, his telecoms group. Some 15,000 TV spots were booked in 15 days. McCann Erikson, the ad agency, said it used tactics usually used to shift fast moving consumer goods, such as washing powder, to appeal to investors on "an emotional and sensory level".

For British observers, there were echoes of the privatisation of British Gas in 1986. That deal came with the famous punchline "if you see Sid, tell him". A £32 million campaign by Young & Rubicam, ensured that Sid – and an estimated 98 per cent of the UK's adult population – got the message. By 1990, Margaret Thatcher's scheme of privatisations had trebled the number of UK shareholders, to more than 11 million.

With several more "mega public offerings" due in coming months, including that of Lodha Builders, which is set to raise £1 billion, Mr Ambani may have led India to a similar tipping point. Local brokers report signing up as many new clients in the fortnight ahead of the RPower IPO as in the previous six months.

Many new investors regard RPower a sure bet. "Ambani is a very big man, [The IPO] cannot fail," said Ajit Burman, a worker in a Bombay newsagent who earns about 6,000 rupees (£80) a month and teamed up with three friends to participate.

On the street, Mr Ambani's charisma looks to have offset the doubts some analysts are voicing. The prospectus listed 66 risk factors - "probably some kind of record in itself," one banker said. They include the warning that "we currently have no power plants in operation or other revenue-generating operations, and we have no significant operating history from which you can evaluate our business".

Indeed, with India's stock market suffering record falls last week amid fears of a US slowdown, it sometimes appeared that Mr Ambani, one of India's most media-savvay - and sprightliest - corporate moguls, had timed the IPO to coincide with his participation in yesterday's Mumbai marathon.

Daily updates on his training peppered India's front pages and TV bulletins. "I have seen Anil Ambani on TV and he has a great personality," Priya Khan, a housewife investor, said.

Media spend - 300 million rupees (£4million)

on:

15,000 TV spots

Ads in 60 publications

8,000 radio ads on 54 channels

2,000 billboards

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