With sterling notes in one pocket and a few euros in the other, from January 1st British shoppers will have the choice of whether to pay in pounds and pence or the new notes and coins of the single currency.
This is the curious phenomenon known as "euro creep" by which the euro will become a parallel currency to sterling - even though Britain has not, as yet, entered the euro zone.
With only 18 days to go until e-day, a growing number of British retailers are joining big players on the high street such as Marks & Spencer, Sainsbury and WHSmith in deciding it makes economic sense to accept the single currency when it becomes legal tender.
This is nothing short of an economic revolution which amounts to introduction of the euro by stealth - and it now looks as if the new currency will operate as a kind of unofficial second currency.
The political implications of this commercial decision for the pro and anti-euro camps are far-reaching. Both sides are already trying to spin the "euro creep" message. Rather than see it as a threat, the anti-euro "Business for Sterling" campaign is busy dismissing the parallel currency theory as a "seven-day wonder" and "hype".
Unsurprisingly, the pro-euro "Britain in Europe" group cannot believe its luck that the single currency will soon be an economic reality in Britain. So, what are the practical implications for British shoppers and voters, the majority of whom are opposed to joining the single currency?
Prompted by a mixture of economic savvy and retail commonsense, the famous Knightsbridge store, Harrods, has been preparing for the euro for two years.
As an exclusive retailer catering mainly for expensive foreign clients, Harrods has long reflected the nationality and preference of big-spending customers by accepting US dollars. "The euro won't pose any problems," says Mr Peter Willis, director of corporate communications at Harrods.
"It will be exactly the same as taking dollars. The preparation for the euro was just a case of getting a new currency stored in the memory bank of our central computer and allowing all 800 tills to accept the euro at the same time."
In keeping with Harrods' low-key, expensive chic, there won't be hundreds of ugly signs advertising euro cash tills. Instead, customers wishing to pay in euro notes - Harrods will not be accepting euro coins - will be informed at the till that they may pay with the single currency. Change will be given in sterling, while all staff attended training sessions to recognise the security features on the euro notes so that they could detect counterfeit notes.
For the store once described as the "nation's shopkeeper," Harrods accepts that if taking the euro is the difference between making a sale or not making a sale, then why not take the money?
Most Britons, however, are much more likely to come across the euro in the supermarket or at airports. From next year, when British holidaymakers return from their summer break or weekend away, they will be able to spend the spare euro notes and coins in their pockets in high street stores. Instead of having lots of European coins and notes stuffed at the back of a drawer, Britons will be able to spend their euros in the supermarket and it will be a case of "familiarity breeds consent" to the single currency.
At least that is the argument put forward by the pro-euro camp. The extent to which holidaymakers have any money left over from their summer break to spend when they get home is debatable. The pro-euro camp accepts this but hopes that even the presence of the euro in Britain will promote an air of inevitability about joining the single currency.
"It is a god-send to the pro-euro camp," says Mr Simon Buckby, director of the Britain in Europe group, referring to the effect of "euro creep" on the single currency campaign in Britain. "Anti-Europeans may try to keep Britain out of the euro, but they can't keep the euro out of Britain. It is not so much the euro itself, but is the fact that it exists and people know they could use it, that is the revolution. It is the subliminal message that will start taking over."
The high street retailer will play a vital part in underpinning that "subliminal" message. The electrical retailer, Dixons, will accept euro notes and coins in its 13 airport stores and "at a pinch" in its main Oxford Street store in London.
It makes economic sense to accept the euro, Dixons says, despite the fact that its chairman, Sir Stanley Kalms, is treasurer of the Business for Sterling group. Sainsbury, the DIY group, B&Q, Somerfield and Kwik Save supermarkets have all introduced trolleys with coin slots that accept euros.
One of Britain's largest companies, British Telecom, is planning to convert thousands of telephone boxes so they can take the single currency, and companies such as Unilever and Toyota, which employ thousands of people in Britain, are asking suppliers to invoice them in euros. Meanwhile, the silent march toward the euro continues at key tourist attractions such as Chessington Zoo and the Alton Towers entertainment park.
Another interesting aspect of "euro creep" is that in one region of the UK a dual currency system has operated for years. In Northern Ireland, many stores have accepted sterling and the punt as legal tender for more than 30 years and will continue that tradition by accepting the euro next year. But the principled opposition of Northern businessman Mr Bill Jeffrey to closer economic ties with Europe is based on a reluctance to give up economic integrity to "nameless, faceless mandarins".
Mr Jeffrey is a member of the anti-euro, Business for Sterling group, but he will accept the euro or any other currency because he believes it will make little difference to business transactions.
"It is a piece of imagination that people will come back from their holidays with lots of euros ready to spend. It has been massively over-hyped and it is inevitable that we are moving towards a cashless society," he says.
"Small retailers here will look after old people in shops so that they aren't confused by coins and notes and the bed and breakfast trade here is very organised - people have been booking online for years. Italians come here with Visa cards, not big wads of liras. So the problem with this is fraud and money laundering, where we are cursed with paramilitary rule and abuse. There are reports of interest free loans over Christmas of £3,000-£4,000 provided that the money is paid back in euros."
In his speech at the European Institute in Birmingham last month, the British Prime Minister, Mr Tony Blair, took time out from the "war" against terrorism to speak about the "tragedy" of Britain's missed opportunities in Europe. Failure to appreciate the "emerging reality of European integration," he said, was a consistent failure of British political leaders. Making the case for closer European integration, Mr Blair held back on announcing the date of a referendum on membership of the single currency.
Mr Blair clearly supports membership of the single currency, whatever his disagreements with his Chancellor, Mr Gordon Brown. Whitehall figures are already briefing about the reality of "euro creep" and the part it will play in a pro-euro campaign ahead of a referendum.
But as far as the anti-euro camp is concerned, the informal appearance of the euro in Britain will not compromise their message. "We think it will show Britain can have the best of both worlds," says Business for Sterling.
"People can pay in euros, but we'll still keep control of our interest rates and economy. But actually, we believe this has been over-hyped and many British people won't spend their euros after their holidays because they will probably be going back to Europe again."
Although he acknowledges two-thirds of Britons are against joining the single currency, Mr Buckby says hostility to the euro "is a mile wide, but an inch thick". Ideological opposition among this group, he says, is shallow - if not non-existent. Therefore, the task for the Labour government and his organisation is not so much a battle over ideology, but to convince naysayers that if it makes economic sense to join the euro, then Britain should hurry up and get on with it.
Britain may not be in the euro zone, but the battle for the hearts and minds of voters has already been joined on the high street.
