A terrible, terrible thing has happened.

As if things in my dietary existence weren't bad enough, I had a further upset a little over two hours ago. Feeling ill and full of self-pity, I went out to forage for some lunch. The terrain near my workplace is heaving with familiar options, but I had heard talk of a new place around the corner, and innocently made my way towards it today, fully unaware of the nightmare that awaited me therein.

As soon as I stepped over the threshold I knew I had committed an appalling error. The place was rammed full of heavily satisfied customers. It was sparkling clean. And the brightly lit, glass-fronted counter winched me in, displaying its wares like a vindictive peacock. In front of me was a vast selection of the most tantalising, the most inventive, the most drool-forming sandwiches I have ever seen in this or any world. In fact, to call them sandwiches would be to do them a disservice. These were beyond sandwiches. They were masterpieces of sandwich craft, the Platonic ideal sandwich, the uberwich. I felt nervous and humble in their presence, so obvious was their greatness. It was unclear whether I should buy one or bow down.

For a while, I did neither, merely standing slack-jawed in front of the display cabinet examining my options. Did I want the one with the sunblushed tomatoes, charcuterie meat, mozzarella slabs and avocado fanned out atop feather soft brioche? Or the perfectly-pink roast beef wafers rippling among a duvet of rosemary loaf? Like a rabbit in the headlights, I was unable to move, well aware that any choice would be my downfall but utterly powerless to leave. Eventually, I chose the tuna melt, reasoning that its lack of red meat made it a 'healthy option' and choosing to ignore the fat implications of the word 'melt'. The speed at which I returned to my desk must surely have counterbalanced the imminent weight gain in a small way. Unwrapping the paper bag's contents, I was well aware that I was stepping into an abyss.

The first bite was like some sort of edible joke. It far outstripped any mouthful of any lunch I have ever had in my life. The bread was ostensibly foccacia, but as foccacia should surely be - not rubbery and cakey, but thin, salty, floppy and flavoursome. And of course, there was tuna and mayonnaise and melt, but there was also tomato, small chunks of aubergine, spinach leaves and tarragon. I don't even LIKE tarragon but in this combination I was confused and delighted. It would be a lie to say that I wept, but for the five minutes that it took for me to eat that sandwich, I was as close as I've ever been to a Damascene conversion.

And now there is, of course, no going back. I can vomit up the sandwich, but I can never not have eaten it. Forever, there will be the memory, not just of the tuna melt, but of the other sandwiches on offer at that glorious place, so close by, with its friendly staff and ability to accept card payments. From this day onwards, lunch will be an eternal battle of self-will, one that I will inevitably lose (and yet win) day after day until I explode or go broke. No longer is the Breakfast Bowl in Pret my biggest temptation. Kids, we have a new enemy in town. If you are passing through the City and are in need of a coronary for any reason, I could not recommend Birley's highly enough. But if you fancy remaining at a safe weight, then stay the hell away from there. It's too late for me, but please, for the love of god, save yourselves.