So how do shops react when you offer to pay in euros? We set out with a wad.
The message from 11 Downing Street may be "not yet", but in London's West End some retailers are already on the money when it comes to the euro.
Shoppers from the Continent are warmly welcomed at the Regent Street branch of men's outfitter Ciro Citterio, where a sign in the window announces customers can "pay here in euros".
Manager Jeffrey Elliot estimates an astonishing 20% of cash transactions in his shop are in euros. His staff also accept US dollars and Japanese yen, although they see less of these.
"We're in tourist heartland here. It's just good business sense because we would be losing money if we only took payment in pounds."
Gordon Brown would like to see that spirit of flexibility across British commerce. After all, our ability to adapt to the challenges of the single currency is one of his five key tests, and one of the four which, according to the chancellor, we have yet to pass.
Since the single currency hit the streets of Europe 18 months ago, several big-name British high street stores have agreed to accept it.
Peter Hain, Europe minister at the time of the change-over, said it was "striking that shops and retail outlets are rushing to use the euro".
Marks for euros
But now the hype has died down, how welcome are euro notes and coins on the British high street? I decided to put the single currency to the test.
Chewing it over, with a pain au chocolat The pro-euro pressure group, Britain in Europe, trumpets 50 leading British retailers which accept euros in some or all of their British stores.
Among the most high-profile is Marks and Spencer, so where better to start, than its flagship store in Marble Arch, London. The cashier is reassuringly unfazed when I tender a five euro note for a 55p pain au chocolat. The till does all the necessary calculations, clocks the pastry at 82 cents and my change comes back in Sterling.
Up the road at HMV, things are a little less smooth when I proffer euros in exchange for the new Radiohead CD. Andrew, the cashier, has to resort to an instruction card, but it's nothing more than a short delay.
He looks on this as welcome challenge. "Working on the tills can be quite a boring job, so something like this means you have to think," he says.
Gap in the market
But while shops like Dixons, Tie Rack and Miss Selfridge are euro friendly, on Oxford Street at least, other big names like Boots, JD Sports, Starbucks and Zara are not. At The Gap in Oxford Circus, garments are priced in pounds and euros, but the latter is not welcome.
Euro friendly: Buskers Mat Ricardo and Ben Danger And while shops like Pied ? Terre and French Connection are happy to play up the French cachet, they're not interested in French cash.
Even in the tourist Mecca of Covent Garden, shops like the Disney Store and the Gadget Shop take sterling or nothing.
But the area's renowned street performers sometimes have no choice.
"We get a few [euros] in the hat now and then," says juggler Mat Ricardo. "It's a hassle, but with the notes you can spend them in Marks. The coins you can't exchange, so we keep them for when we go to the Continent."
'Prices would rise'
Tony Wright, who runs a magazine stand in Piccadilly Circus, is less keen. "I've taken the odd couple of euros but really it's too much aggravation with the conversion. So I've turned some people away," he says.
Paying in euros does not guarantee a good exchange rate And even though a single currency would undoubtedly make good business sense for him, his heart rules his head.
"I don't want it. My mum remembers when we went to decimalisation that everything shot up in price then. The same will happen if we go into the euro."
London, like the rest of Britain, is clearly divided on the matter. But what about those outside the city?
The people of Pound Green in East Sussex perhaps have more to lose from the single currency than most of us, although the name derives not from Britain's historic currency, but a pound where farmers used to tie-up their livestock on the way to market.
Russell Horscroft, a mechanic at Pound Green motors, have never been offered euros by a customer, if he was... "I'd be fine about it. It's just a matter of a quick sum to convert it."
Russell Horscroft: 'I'd be fine about taking euros.' "Practically, I think the euro is a good idea." says his colleague Barry Anscombe. "Britain is expensive, so it should mean that prices will fall. But I think shops will use it as an excuse to put prices up."
Pound Green resident and retiree Jennifer Russell could be won over to the euro. She and husband Alan have a holiday home in northern Spain, so one currency would make life simpler for them.
"It's already simplified things on holiday. We're 45 minutes drive to the French border, so we can go over there and stock up with wine without any thought," she says.
'Not yet, anyway'
Husband Alan is more sceptical. "Practically the euro makes sense and I've no emotional attachment to the pound. But politically, I wouldn't trust the Germans and the French to run things.
"To be honest, I haven't made up my mind because I don't know enough about it. I need to find out all the facts."
Down the road from Pound Green, at Buxted Stores, my offer of a five euro note in exchange for a chocolate bar is met with an embarrassed giggle.
"We don't take those I'm afraid. Not yet, anyway."