Zimbabwe's sham election has triggered yet more calls for action to be taken against the Mugabe regime. The possibility of armed intervention has been raised in serious quarters: if we can go into Sierra Leone, Kosovo and Iraq, why not Zimbabwe? This is a non-starter. For one thing, the British – as the former colonial power – are in no position to turn back that particular clock. Nor, I suspect, do they have the troops available.

Also at play in this argument, I fear, is an understandable denial of personal responsibility. Calling for an invasion, and then complaining when the Government fails to provide it, offers a comforting sort of moral let-out. And the point is not intended cheaply. Personal responsibility has a role to play here. A great many people in Britain have direct or indirect financial investments in Zimbabwe. How can they denounce the increasing repression in the country but continue to invest in businesses that make their profits in such an environment?

A divestment campaign aimed at crippling the Mugabe regime's finances is growing. Activist groups are identifying UK and other foreign businesses still operating in Zimbabwe and are putting pressure on them to divest or change their ways. They are calling on shareholders to ask whether their money is underwriting Mugabe's atrocities. Tesco shareholders were last Friday accused of profiteering from vegetable imports from Zimbabwe "watered by blood". And a subsidiary of the media giant Naspers was compelled to return the money it made from a print job it did for Mugabe's election campaign when activists called the profits "blood money" and demanded that they make Zimbabwean blood and pain count on their bottom line.

Britons seem surprised to find that Barclays Bank and Standard Chartered still provide loans and invest in government bills that indirectly enable Mugabe to finance his repressive system of government. They will be even more surprised, I suspect, to learn that Dominic Grieve and other MPs are involved in companies dealing in the country. In fact, all multinational businesses operating in Zimbabwe directly subsidise Mugabe's network of thuggery. The government's currency control regime means that almost a quarter of all hard currency traded in and out of Zimbabwe is more or less given for free to Mugabe's central bank. If you do business in Zimbabwe you cannot avoid it. If Mugabe openly seized a quarter of all hard currency, there would be an international outcry.

However he gets his money, it goes to pay for an elaborate system of oppression. He has to pay the army and police before they arrest the democrats. He has to pay the thugs who beat his opposition and, finally, he has to pay off the party loyalists who would otherwise be tempted to depose him for his gross mismanagement of the economy. None of them want to be paid in worthless Zimbabwean dollars. It is only through the expropriation of hard currency that he is able to keep his system operating.

But business leaders have long argued that economic sanctions – the United States and European Union are already imposing some on Zimbabwe – rarely produce changes in foreign governments and instead hurt the poor. They say that pulling out will only further harm the people of Zimbabwe who are suffering not only from state repression but also from hyper-inflation and near total unemployment. Cutting off the inflow of foreign cash will not be without its costs, but it will damage Mugabe. Not many effective measures can be taken, but he needs to be made to feel uncomfortable and this is the best available way. To those who say that continued engagement and talking will eventually produce results, I say this: if you have been really trying – rather than going through the motions – your time is up.

Tesco says the farmers from whom they import employ almost 4,000 Zimbabweans, and that they are helping them survive. Tesco says it pays the farmers directly via South Africa. But all that does is force the farmers to create elaborate avoidance schemes to bring the currency into Zimbabwe. Financial institutions such as Barclays, on the other hand, have no choice but to transact within Mugabe's system.

Economic sanctions often fail. Historians tell us that the closest they have come to success may have been in toppling the apartheid government of South Africa. But even there, ordinary black South Africans suffered immensely. In places such as Cuba and Burma they have done nothing to dislodge the governments. But Zimbabwe may be an exception. A reduction of foreign currency flows from business will choke Mugabe. And perhaps force him to the negotiating table.

Mugabe probably would not capitulate just because Tesco cuts contracts with a few suppliers in Zimbabwe. Equally, though, we are entitled to expect some sort of moral stand from large corporations. After all, they are no slouches in demanding the same from governments. Expecting governments to wave a wand and solve the problem is a form of moral hand-washing.

Equally, though, we are entitled to expect some form of leadership, which is why the shadow ministers and MPs named in today's Independent on Sunday – who should know better than anyone that leverage lies at the corporate level – are open to censure. Acting collectively, if necessary, companies investing in Zimbabwe could put enormous pressure on Mugabe.

Removing Mugabe's knighthood or preventing the Zimbabwe cricket team from playing in the UK will not force Mugabe or the so-called "criminal cabal" to shift from their hardened positions. That would be too easy. What is likely to work are measured actions that will threaten or sever Mugabe's financial lifeline – tough measures that might hurt the pocketbooks of individual shareholders in the West. If individuals in this country want to exercise their leverage over Mugabe, they must be prepared to face up to the contribution of British business to his system of tyranny. In the search for effective punitive measures against Mugabe, tough decisions must be taken by all.

Gugulethu Moyo is a Zimbabwean lawyer working for the International Bar Association. She is the co-author of 'The Day After Mugabe'