"It all started with semen from Blackmore bulls,” Michael Reid casually tells me in between strips of Highland Wagyu beef. “And an egg, of course.” If the 40-day aged ribeye mid-chew in my mouth wasn’t ephemerally tender, I could have choked. Don’t get me wrong, I’m just as interested in the genetics of cows as the next guy (ahem), but in the sleek setting of M Restaurant’s Threadneedle Street dining room, you might say I was caught unawares. Then again, all love stories – even those of a meat lover – have to begin somewhere, and this one starts with the prized embryos of David Blackmore’s 100% full-blood wagyu beef in Australia.

If Reid isn’t a household name just yet (recent TV appearances on Great British Menu, Saturday Kitchen and Sunday Brunch won’t hurt), his role in M Restaurant’s rise from neat concept to genuine contender for London’s most stylish restaurant chain has been crucial.

Reid was a prolific stagiaire in some of the world’s best restaurants, but it’s his knowledge and passion for beef that has contributed most to his and M’s rising stocks. While a cynic might sniff at ‘just another steakhouse’, one look at the bovine ageing in the restaurant’s meat room is enough to show how deeply Reid cares about his product. It took the chef four months and hundreds of tastings to assemble his steak list from the world’s greatest producers of beef, but the result is London’s best selection: the aforementioned Blackmore wagyu sirloin – “the best wagyu in the world, bar none,” Reid says – Kobe beef fillet from Japan and Botswana ribeye to name a few cuts.

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Now, wondering where all that bull semen ended up? (Stop giggling at the back.) The answer is Highland Wagyu in Perthshire – the passion project of Mohsin Altajir and Martine Chapman. The beef duo met at Blackmore in 2011, and purchased seven of famed Australian cattle breeder’s full-blood wagyu heifers, two bulls and the embryos to start their own herd. Fast forward six years and you’re looking at Britain’s best and most valuable beef product – it’s Reid’s prized steak, and what I’ve joined him to taste.

“When you drink a glass of great red wine, there’s this depth of flavour: it coats your palate and you get none of the bad tannins,” Reid explains, as we slice through buttery portions of aged ribeye and rump cap. “It’s the same with wagyu. The low quality stuff hasn’t had the same level of care, it just tastes fatty and oily – there’s no flavour there.”

It took four months and hundreds of tastings to assemble the world's best beef on one menu

Other than Blackmore genetics, the secret to Highland Wagyu’s success comes from handfeeding its herd for up to 36 months with seaweed and Omega 3. It creates exceptional marbling of fat typical in the best wagyu, which in turn gives the meat its buttery, sweet and succulent texture. The proof is in the eating.

It isn’t just delicious, though – this is also exceptionally rare beef: the tiny Scottish outfit slaughters just a single 100% full-blood wagyu head a week, and Reid gets the whole thing.

Fighting off competition from the likes of Hawksmoor, Reid convinced Altajir and Chapman to choose M as the only restaurant in the world to serve Highland’s finest through his ingenious secondary and offcut-centred recipes.

Bone marrow popcorn arrives at the table, then wagyu biltong, then wagyu reuben sliders – it’s an eye-opening, belt-testing feast, but my stomach isn’t complaining. “I’m working on a wagyu kebab next,” Reid smirks. I’m getting meat sweats just thinking about it.

For more information, see mrestaurants.co.uk