IT is always an awkward moment.

There you are in Starbucks, having ordered a mocha chocca cappuccino with added sparklers, and the barista/unemployed arts graduate asks you for a sum an energy supplier might find excessive.

Instead of fumbling for more change, try striking a deal. Say that while you are grateful for the beverage, the money to pay for it is coming from a bank account in Luxembourg, where tax rates are lower. In light of this, you will only be paying a fraction of the price other UK customers will hand over. Don't be offended when the barista asks for your name to put on the side of the paper cup and it later turns out to be "Chancer".

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Observers at the Public Accounts Committee in the Commons this week were given quite the lesson in international tax etiquette as observed by Starbucks, Amazon and Google. Despite earning lots of money in the UK, these US giants of commerce pay relative bags of beans in taxes.

Take Amazon, for example. One MP, Charlie Elphicke, reckons it sold £3.9 billion of goods in the UK last year. On this, it paid £1.9 million in UK tax. Google had UK sales of £2.6 billion and paid £6 million in tax. In the 14 years since Starbucks sold its first coffee here it has handed the Treasury £8.6 million in tax.

It hardly takes an accountant to see that this doesn't add up. Under a clever little system of their devising, these companies and others move profits around the world so that they pay tax in a country of their choosing. It's all perfectly legal. Strangely enough, the chosen countries turn out to be low-tax havens, such as Ireland or Luxembourg. The UK, this sceptred isle, has become Treasure Island, with firms plundering our pounds and scarpering with the riches. They pay tax on it, of course they do. It's just not our rate of tax.

As is the British way, consumers, politicians and other businesses have been slow to grumble. Until now. Margaret Hodge, the Labour chair of the Public Accounts Committee, was in the mood to dispense black spots and tax demands all round this week when executives from the three US firms gave evidence. One witness, an Amazon chap, was accused of spouting "unacceptable nonsense". Not a good customer review there, then. When the suits tried to argue their case back, pointing out that everything they did was in accordance with the law, Ms Hodge countered: "We are not accusing you of being illegal. We are accusing you of being immoral." Had one searched Google at that point for "faces as red as a skelped backside", pictures of the hapless executives would have come up.

It is not just MPs who have noticed that these firms have a case to answer. Andy Street, the managing director of John Lewis, has pointed out that paying less tax here means the likes of Amazon can invest more and ultimately sell more than a company paying British tax rates. The playing field, far from being level, is tilted in favour of the avoiders.

Chancellor George Osborne is not happy either. In Mexico last week, at a summit of G20 finance ministers, Mr Osborne and Germany's Finance Minister Wolfgang Schaeuble said international tax standards had not kept pace with changes in global business practices, particularly e-commerce. "Britain and Germany," the two concluded, "want competitive corporate tax systems that attract global companies to our countries, but also want global companies to pay those taxes".

This is quietly revolutionary stuff, if acted upon. The key word here, of course, is "if". Governments know they cannot push multinational firms too hard otherwise it is not just profits that could be heading overseas – jobs might follow too. All governments live in terror of firms taking fright and flight. Witness the headlines this week when Royal Bank of Scotland said it might consider upping sticks if having its HQ in an independent Scotland brought the firm "extra difficulties".

Given the state of western economies, and how long it is going to take for us to get back to pre-crash levels of prosperity, it is a brave government that would pick a fight with a firm that brings in jobs. Amazon, for instance, employs 15,000 people directly in the UK, a significant number of them in Scotland. These workers, in turn, keep thousands of other staff in work indirectly. They all pay their taxes.

Faced with the risk of job flight, governments might be content for now to talk the talk on tax avoidance but do nothing lest firms walk the walk and go elsewhere. That, then, leaves it up to consumers to decide whether they want to take action. One grassroots movement, UK Uncut, is calling for protests at Starbucks next month.

It will be true pulse-of-the-nation stuff to see how many protesters turn up. When it comes to being mad as hell and unwilling to take any more, the average consumer and taxpayer has a vast range of targets to choose from. Tax-avoiding multimillionaire comedians, anyone? Prison-avoiding, expenses-fiddling MPs? Bonus-grabbing bankers? Executives awarding themselves obscene wage rises? When it comes to having people to get mad at, we plebs have never had it so good.

It is doubtful that Amazon, Google and Starbucks are top of the list of firms and individuals who give consumers the pip. Customers are keen on these companies for the simple reason that they provide relatively good service. For anyone who works on the road, Starbucks, with its sockets galore, is a pal. Google delivers in seconds. Amazon's customer service, in my experience, is hard to fault. After reporting a broken Kindle recently a replacement was delivered the next day. If you've tried to buy someone a Kindle Paperwhite for Christmas you'll know that such is the level of demand the goods won't be despatching until mid-December. If consumers are mad at Amazon, they have a funny way of showing it.

Reform has to come, however. Loopholes must close, and on a global scale. It is a basic question of fairness, the stuff the Coalition Government is so keen to promote. Too many of these firms have been too greedy for too long. Long enough for MPs and chancellors to wake up and smell the cinnamon sprinkles. Long enough for consumers, if not now, then soon, to beginning looking on these brands less favourably. If provoked enough, even the eternally reasonable inhabitants of Treasure Island will tell a firm to walk the plank.