In the practice it's very straightforward as roles are clearly established. ‘Hello, I'm the patient’, ‘Hello, I'm the dental nurse’ (for which, read any member of the dental team). One probably wears some sort of identifying clothing; a white coat perhaps or a dashing, over the shoulder, buttoning down the side, light avocado pastel number with matching socks. The other wears ordinary clothes. So far, so good.

The problems arise when we transpose the situation to, say, a supermarket. Late night in Tesco perhaps, Saturday morning in Sainsbury's if you prefer. You are slouching around the tinned goods just off the cereals aisle when who should you chance to bump into but a patient? But of course here lies the complication because right now they are not a patient at all, just another shopper, so the ‘Hello I'm a dental hygienist’ thing doesn't much work anymore, except that they still think of you in that role. ‘Hello, how funny that we're both reaching for the pilchards in tomato sauce – do you have them on toast? We always do when we're watching Dr Who.’

Even for the most experienced professional it is still a moment of some frisson. To suddenly realise that your frozen vegetable buying habits are under direct scrutiny sends more of a shiver down the spine than a flash-chilled pea ever could. You can immediately hear the next conversation going on at some street corner ‘you'll never guess who I've just run into … and she had a trolley load of those minted ones, yes, the most expensive that's right … and they say dentistry doesn't pay.’

The matter of clothing is no longer a form of modified security either. As if naked before the court you are the one judged to have equally ‘ordinary’ clothes now, every detail being logged for future use. ‘Torn denim jeans, a t-shirt from Thorpe Park dated 2002 and Co-op trainers. You'd have thought she'd have had Nike at least.’

Now that you know that the ‘patient’ is in the shop even worse things happen. Try attempting to put that pack of chocolate biscuits in your basket now without an overwhelming wave of guilt. Purchase of confectionery is ruled totally out of the question despite what might be on the shopping list and carbonated soft drinks have to be sprinted past with an assumed air of preoccupation in searching for the bottled water.

There are even more unnerving possibilities though. A long looked forward to weekend away with your partner. You've just had a wonderful lunch, a light snooze and then an invigorating walk across the moors, or over the dales or even round a stately home. Back in your room, you kick off your lightly scuffed walking shoes and settle into the deep warm luxury of the monogrammed towelling robe as you mooch off to the health spa. Just at the moment when you are tucking some slightly flabby bits back into your swimming costume at the poolside; at the instant when you are sublimely wrinkled in the Jacuzzi; in the twinkling when you've just decided to go Scandinavian in the sauna, take everything off and have a tentative thwack with the birch twigs – it happens. ‘Hello, I'm a patient at your practice.’ There is nothing you can do, nothing to redeem yourself. And don't even think of asking how their pinned amalgam is holding up.

Most crushingly comes the airport departure lounge. A mere ten minutes into what turns out to be a delay of hours because of fog, ice, sunstroke, mechanical failure, anything irritating after a fraught drive to the airport, who should you see but your patient. And quite possibly your least favourite one. And his wife and their three awful children. The agony here is that you have no idea how long it is really going to be. In Somerfield's by the vegetables it can be a 30 second pleasantry or a two minute sympathetic ear. Even in a hotel steam room you can go ‘phew’ and leave for the sanctuary of the plunge pool but here it could be 20 minutes, three hours and a quarter, or an overnight ordeal on the checker-marked, carpet covered seating. You are totally deprived of all the familiarities. The conventional world has abandoned you.

Eventually the plane arrives, the luggage is loaded and you board. A little respite until, in the empty seat next to you… ‘Well, what a coincidence. I'll bet you didn't expect to be seeing me again so soon.’

Never mind, back at the bastion of the surgery it is all forgotten and forgiven, the security of the familiar inside dismisses the ghastliness of the unguarded moment outside. Well, almost. Almost, because things are never going to be quite the same again. Unspoken, of course, but lying very close under the surface: ‘Hello, I'm the receptionist (who you saw in a baggy pair of orange sweat pants)’. ‘Hello, I'm the patient (who has intimate knowledge of your freezer compartment).’ It's good seeing patients isn't it?