On 27th October 1986 the London Stock Exchange (LSE) introduced reforms which would alter the way it worked for ever.
In the name of deregulation, the LSE abolished fixed commission charges and introduced changes which smoothed the way to telephone and computer-based trading.
The strict separation of jobbers, the market's middlemen and stockbrokers was removed.
Other changes in what was know as the Big Bang saw the welcoming of investment from overseas.
Since Big Bang many of the City's historic companies have been taken over by American, European and Japanese firms.
The greater competition and higher investment are credited by many with helping secure London's now undisputed position as the world's number two financial centre.
Exports of financial services reached £20 billion in 2003, according to the Treasury, making a major contribution to the country's balance of payments.
"Following Big Bang, there was a great movement of international business into the UK market," Peter Thomson, chief executive of Taylor Young Investment Management, said.
"This set London up and stabilised it as a financial centre worldwide," he added
Sir Nicholas Goodison was chairman of the London Stock Exchange at the time, and oversaw the reforms.
"It caused a huge growth in the market," he told Working Lunch.
"Without the changes the markets would have looked elsewhere."
For hundreds of years the City was effectively a closed shop with few brokers allowed in the market.
A private investor of 1986 would be amazed at the choice and low prices offered by stockbrokers today.
"Before Big Bang the City was a cartel," Justin Urquhart Stewart of Seven Investment Management said.
"There was an enormous change and a lot more competition for the better and above all for the investor."