He laughed and moved off as our eyes met: he'd almost been caught in the act. I was not so soft a target as they presumed. I had, after all, spent that morning discussing the rise in shop crime at Christmas with the experts - and had them to thank for hiding my purse at the bottom of my bag.
Unfortunately, there is nothing exceptional about this experience. Christmas is notorious as the best time to steal from shops and shoppers.
"There's a dramatic increase in theft at Christmas. Stores are busier, there are more temporary workers who are less well trained in how to spot thieves, the shops are fuller and staff more tied up," explained Phil Edwards, seconded from Dixons to the Home Office as business adviser to the Crime Prevention Unit.
For, as the ranks of genuine shoppers swell, so do those of the shopping underworld, many of them perfecting their light-fingered lifts long before the average shopper might expect. "Thieves take the old phrase 'shopping early for Christmas' very seriously," says Bob Goslin, group security controller at W H Smith and a former police officer. "They start at the end of October so they can sell goods on for Christmas. The increase is significant in retail and other types of crime. There's more opportunity to pass on goods and therefore the problems increase."
But retailers and police do not have an image of a typical thief in mind: it really can be anyone. They might be working in groups or alone; be young, old or middle-aged; male or female; well dressed or scruffy, as another security chief, Stuart Campbell of Selfridges, is keen to point out. "It's across the whole spectrum. We even have experience of a 'family' with a child in a pushchair. The child isn't stealing, but is a method of providing cover. The adult puts something in a bag on the pushchair and transfers it to the pillow under the child."
The idea of children being used to steal their own Christmas presents may seem abhorrent, but Fagins, it would seem, are as commonplace today as they were in Dickensian times. As laws on juvenile crime make it impossible to prosecute children under 12, so unscrupulous or impoverished parents can take advantage. "Sure, kids steal their own Christmas presents from the age of eight upwards," says Mr Goslin. "And some of the younger ones are clearly used by their parents because they can't be prosecuted."
Christmas is an open invitation to people to steal, as stores are stocked high with luxurious looking goodies, temptingly displayed. While this works effectively in stimulating our spending buds, it rubs in the fact not everyone can afford what they'd like. That's how professional thieves can drum up such a roaring trade each year.
"Professionals steal because other people want to buy Christmas presents cheaper," added Mr Goslin. "They sell them on and even steal to order. What happens is someone in the pub will say 'Can you get me a radio or a high value pen? The thief will bring it in the next night." Car boot sales are another popular outlet for the pros.
Professional thieves can make a hefty profit, as they think nothing of walking out of a shop with 20 or 30 items. Sometimes, they go to the trouble of dressing up as staff members. Overcoats are stuffed with goods, empty shopping bags crammed with items, bags lined with tinfoil to stop electronic tagging systems from activating. In one up-market shop, the shop assistant turned his back to discover a whole table of silk/cashmere scarves wiped clean away: they turned up later in a black bin liner out the back, disguised as rubbish for an evening pick-up.
Electrical goods and clothes are popular items for the light fingered. But, according to research released this week by the Home Office, not quite as desirable as food, alcohol and tobacco.
But, they are not all taken by shop-theft specialists. Yuletide brings out another breed: normal shoppers who would never consider themselves criminals. Suddenly, as the lights twinkle and their arms ache under the weight of carrier bags, they snap.
"It may be frustration in attracting a shop assistant in order to pay," says Mr Campbell."Some people may walk out of the shop, but some will steal. My personal view is that opportunist crime rises in this season so we try to ensure that we have sufficient staff to cater for that."
Others might do it for the kick. Whatever their motivation, naughty novices, unlike their professional counterparts, want small, easily concealable goods such as accessories, leather goods and gloves. And they often don't consider the consequences. "There's a misconception that unless they leave the store, they can't be arrested and prosecuted," says Mr Campbell. "That's totally wrong. We will arrest and prosecute if we can show sufficient evidence."
And, with a growing number of CCTV cameras, exit bleepers and uniformed and plain-clothed security guards, getting away with a casual theft may not be as easy as it looks. Or at least that's the message both stores and police are trying to get across with measures such as opening special mobile police units in shopping centres or main high streets and organising phone-rounds when a notorious thief is spotted.
Whatever the measures, crime costs stores pounds 2.7bn each year, including pounds 580m on security devices, according to the British Retail Consortium. In consumer terms, that's pounds 120 extra on the family shopping bill each year.
At the end of the day, the honest consumer loses all ways round: handbags, purses, and increased prices of goods. It's almost enough to send you down to the car boot sale.