The lucrative Indian legal market - a holy grail for leading City-based international law firms - could be opened up in as little as three years if political conditions are favourable, Bridget Prentice, justice minister, has claimed.

Ms Prentice, who has just returned from a lobbying trip to India, said it would be a "tragedy" if the country's legal industry failed to internationalise like other sectors such as information technology and pharmaceuticals.

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Her comments highlight London's aggressive push for the opening of restricted legal markets such as China, Brazil and India, whose ban on foreign lawyers means it is viewed by top British firms as a final frontier.

Ms Prentice said in an interview that she was trying to support Indian ministers who were in favour of deregulation, reassure lawyers there who had misgivings, and encourage business people to start speaking more loudly about why the change would be good for them.

She said: "Probably now most people in India who are interested in this recognise that it's a matter of when rather than if. And we would say: 'You can do this in three to five years. Don't go down the Japanese route of taking 20 years to do it.' "

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Ms Prentice said the remaining obstacles to opening the market - including an epic court case in which international law firms have been entangled for more than a decade - were not overwhelming. If India held back, it risked "missing the boat" on a change that would give it access to needed legal expertise and increase the opportunities for local lawyers to do international work.

She said: "If they don't get involved in this now ... they may be bypassed. And that would be a tragedy."

India's legal market is seen as the last great land of opportunity for foreign law firms as the country's industries become more global and its companies begin to look to do more deals overseas.

Britain is particularly keen on deregulation because London is home to some of the world's largest and most international law firms, including Clifford Chance, Linklaters, Freshfields Bruckhaus Deringer and Allen & Overy.

Foreign lawyers in India are banned outright from setting up offices in India, and even domestic firms are heavily restricted. They cannot grow in size to beyond 20 partners each, and they cannot incorporate, advertise or tie up with companies outside their profession.

Overseas lawyers have for years tried to work around these tight rules by opening India practices outside the country and then shuttling in to service clients from their hotel rooms, or from the offices of "friendly" domestic firms with which they have formed alliances.

Numerous studies have recommended that India's legal profession be opened if only to rebalance the market, which derives 90 per cent of its revenue from litigation and is pitifully small compared with the size of the economy.

But many Indian lawyers have fiercely opposed the entry of their foreign rivals, arguing they are not prepared for competition from global firms. Some claim that allowing corporatisation will destroy the values of the local industry, turning lawyers into mercenaries.

Mumbai's high court is expected next month to hear a key case filed by the justice ministry that seeks to allow foreign lawyers to practise in India if they stick to advising only on international law.

But even if the ministry wins the high court decision and any subsequent appeal, it is doubtful India's politicians will have the will to stand up to domestic lawyers in the run-up to a general election.