The people at the takeaway were surprised.

"Tuna?" one said, reaching for the container.

For the past few years I’d turned up during my lunch break and ordered tuna baked potato - but that day I didn’t. "Beans and cheese," I replied, having decided after a TV programme on the tuna fishing industry that never again would it pass my lips.

"You’ll never do, it," said a colleague, "You’re a creature of habit." That made me even more determined. Cruelty to tuna aside, I bristled at the idea of being seen in that way. Yet I knew it was true, I am a creature of habit - I eat the same food, shop at the same supermarkets, dress in the same clothes, visit the same places on a weekend, even holiday in the same place.

I’m not alone. I watched a recent documentary about a leading supermarket which revealed that many customers are follow the same route around the store week after week, buying the same items, and presumably making the same meals.

Some of my colleagues are no different, regularly eating the same lunch. I used to joke with one, about her beloved tuna and packet of Hula Hoops. Celebrities are habitual too - earlier this month George Clooney was described as a creature of habit for dating ‘yet another’ cocktail waitress.

I think most people are creatures of habit. Surely it would be too stressful to live lives differently every day. Take moving house, or changing jobs - it always takes a while to settle into it.

That’s not to say we shouldn’t embrace change. I remember one day, my tuna-sandwich-eating workmate brought cheese and pickle. It was a talking point, but more than that it proved that habits, however ingrained, can be altered.

It was with this in mind that I gave up tuna. I was a bit shaky after reading a definition for ‘creature of habit’, as ‘one who is extremely used to their own habits and does not function well without them.’ Would I go to pieces without tuna? As the week went on I admit I did suffer a bit of cold turkey (the condition, not the food), and had to wrack my brains to come up with alternative lunches that I liked.

But, with images of the battered and bruised fish still fresh in my mind, I stuck firm and, although it is early days, believe I have kicked the habit.

Which makes me think that maybe I should introduce some changes. Like ditching the cardigans, trying Chinese food or holidaying abroad. It will have to be gradual - years rather than months. I won’t function well if it’s too fast.