Walk down a gin aisle and you will see three phrases that sound like quality grades: gin, distilled gin and London dry gin. They are not grades. They are legal descriptions of how the bottle was made, and the differences are more interesting than the marketing suggests.
Under EU rules every gin, whatever the label says, must taste mainly of juniper and be bottled at no less than 37.5% alcohol by volume. That is the whole entry ticket. A flavoured pink gin and a bone-dry martini gin both clear it. Everything else is about method.
The plainest category is simply gin. It can be made by taking neutral alcohol and stirring in flavourings, even artificial ones, with no second distillation at all. This is called compounding, and it is closer to making a squash than to distilling.
Next is distilled gin. Here the neutral alcohol has to be redistilled in a still along with natural botanicals such as juniper, coriander seed and citrus peel. Flavourings, sweetener and colour may still be added afterwards, so a distilled gin can taste of botanicals that never went near the still.
At the top sits London gin, usually written London dry gin. It is the strictest. The botanicals must be natural and must do their work during distillation, the distillate must come off the still at 70% alcohol or stronger, nothing may be added afterwards except water and a trace of sweetening, and no colour is allowed. The name describes a method, not a place: a London gin can be made anywhere.
Switch on the things that happened to a gin and see which names it is allowed to carry. The rules are a simplified version of the EU definitions.
Heat releases flavour in a different way from cold infusion. In a still, the vapour of alcohol and water carries the aromatic oils of juniper, coriander and citrus peel with it, and a distiller can separate the harsh early and late parts of the run from the clean middle. That is why distilled gins often taste integrated and rounded: the botanicals have gone through the same process together.
Flavouring added afterwards is quicker and cheaper, and it lets a producer chase flavours that do not survive heat well, such as fresh berries or delicate flowers. Neither route is automatically better. It is simply a different craft, and the label tells you which one you are buying.
London gin is a promise about what was left out: no late flavouring, no colour, hardly any sugar.
In gin, "dry" does not mean low in alcohol or sharp. It means unsweetened. Old Tom gin, a style that is usually lightly sweetened, sits at the other end, and in the middle are gins that are simply not labelled either way. Because London gin allows only a trace of sugar, the word "dry" on the label is a real constraint rather than a mood.
For a Martini or a Gimlet, where the gin is the whole drink, a London dry style is a safe starting point because its flavour is built almost entirely from the still. For a long drink with tonic, soda or fruit, the choice matters much less, and a compounded or flavoured gin can be a lot of fun. For a low-alcohol evening, an alcohol-free spirit with a juniper note and a good tonic gets you most of the way to the same glass.
Enjoy gin in moderation. It is a strong spirit, and a measure of around 25 to 50 ml per drink is plenty.