Does caffeine levels vary by coffee chain?

We are in great debt to Which Magazine, which announced that it had conducted independent tests on caffeine levels in coffee served at a number of famous coffee chains.

So, does caffeine levels vary by coffee chain?

Yes, it's very surprising to say that the caffeine levels in coffees tested at various coffee chains varied enormously.

Which coffee chains served the highest caffeine levels?

According to the Which Survey, Costa Coffee and Pret A Manger served the highest level caffeine in for both cappuccino and espresso as follows:

Cappuccino 350ml  (Pret): 325mg caffeine

Cappuccino 360ml (Costa): 325mg caffeine

Espresso 30ml (Pret): 180mg caffeine

Espresso 30ml (Costa): 100mg caffeine

Which coffee chain served the lowest caffeine levels?

According to the Which Survey, Starbucks served the lowest level caffeine as follows:

Espresso 30ml (Pret): 33mg caffeine

Cappuccino 360ml (Costa): 66mg caffeine

Why is there such a variance in caffeine levels in coffee served at UK coffee chains?

To be honest, these results are surprising and warrant further investigation. It's not clear how many coffees were surveyed and analysed by Which Magazine, so these may be outliers.

Caffeine levels are affected by roast level, grind level, extraction process and dose level (grams of coffee brewed).

But, even when considering those factors, the difference is startling. If this is an accurate appraisal of caffeine levels, then we presume the main reason is that some coffee chains are using more grams of coffee than others to brew their coffee.