Greggs has also officially overtaken Costa as the nation's biggest coffee chain for the first time, meaning there's more steak bakes than ever on the high street.
According to new data released by Allegra World Coffee Portal Project Cafe UK, Greggs added 34 shops to Britain's high streets and shopping centres in the first half of the year to reach a total of 2,737 outlets, compared with Costa's 2,707.
But with both chains having numerous near-identical breakfast, lunch and drink delicacies, which is truly the best choice if you are hoping to save on calories?
A sausage bap from bakery chain Greggs has 377 calories per portion, while Costa's same offering is 515 calories. Likewise, a yogurt with compote from Greggs is 92 calories less than the same popular breakfast item sold at Costa.
The same can also be said for the popular chain's drinks, with Costa's Americano containing double the amount of calories of one served at Greggs, while Costa's hot chocolate is 33 calories greater than its bakery rival.
However, there are instances where Greggs overtakes Costa in its calorie figures - with their chicken flatbread coming to 374 calories, while Costa's offering is less at 339 calories. Their pain au chocolats are also both equally matched at 299 calories.
Greggs have also come under fire for a change of their prices this year - with the cost of their beloved sausage rolls rising to £1.35, while travel hubs such as service stations and airports have seen costs of up to £1.85 or more.
With competition between Greggs and Costa heating up, read on to discover whether Britain's greatest bakery beats the historic high-street cafe in the calories contest....
According to Brenda Heather, a nutrition expert at Meo Nutrition, these figures directly contradict the widespread assumption that a bakery is always an 'indulgence'.
She told the Daily Mail: 'Plenty of shoppers assume the coffee shop is the lighter option and the bakery chain is the indulgence. Your figures suggest that assumption doesn't hold up once you compare like for like.
'The sausage bap stands out significantly. Costa's comes in at 515 calories against Greggs' 377. Pair it with a Costa latte and you're at 661 calories before 9am, compared with 491 at Greggs.
'That 170-calorie gap is about the same as a packet of crisps, and it's easy to miss when it's split across a sandwich and a drink.'
Ms Heather also noted that it was worth paying attention to the gap in calories for the yogurt with compote, noting that many Britons would likely 'see a yogurt pot as the virtuous choice'.
She explained: 'Costa's yogurt with compote contains 206 calories compared with 114 at Greggs, meaning it has around 80 per cent more calories despite both being marketed as similar breakfast options.
'Neither is particularly high in calories on its own, and yogurt can be a perfectly sensible breakfast choice. What I find interesting is how much variation there can be between two products that sound almost identical.
'Differences in portion size, added sugar and toppings can all affect the nutritional profile, so it's worth checking the label rather than assuming you're getting roughly the same thing at different chains.'
Ms Heather also explained that yogurt can quickly grow in calories due to 'toppings such as granola, compote and larger portions can quickly turn a light breakfast into something closer to a full meal'.
And when it comes to drinks, she noted that the number of calories 'matter more than people think', with Costa racking up more calories than Greggs in their Hot Chocolate, Latte and Americano offerings.
However, she stressed that these results do not necessarily mean that Greggs is automatically the 'healthier choice' out of the two food chains.
'Its ham and cheese toastie is 543 calories against Costa's 356, and its croissant is higher too,' she noted.
'A brand's image tells you very little about what's in the paper bag, so checking the calories on the specific item you're buying is the only reliable guide.'
Dr Ramon Velazquez, a Scientific Advisor at Mind Lab Pro, explained that Costa's 'ceramic cups, warm lighting, a higher price point and menu' could initially signify to many that it is a healthier choice.
'Researchers call this the health halo. Once it's active, people consistently underestimate what they're eating, and they often feel licensed to add a little extra because the choice already feels virtuous,' she explained.
'Greggs carries the opposite reputation, so customers there may be more alert to what they're ordering.
'Your exceptions are useful here: the Greggs ham and cheese toastie is heavier than Costa's, which shows that branding predicts perception far better than it predicts the actual numbers.'
However, both experts explained that it is crucial not to focus solely on calories, with the likes of 'fibre, protein, salt and saturated fat' also playing a key role in the 'whole nutritional picture'.
Ms Heather noted: 'I'd encourage people not to get too caught up in calorie differences alone. A slightly higher-calorie breakfast might offer more protein or keep you satisfied for longer, so it's always worth looking at the bigger nutritional picture.
'Calories are the quickest way to judge whether a grab-and-go breakfast fits into the rest of your day.
'A simple habit helps: choose the smaller drink size, skip the extra toppings and compare the calories on the label before you pay.'