There are 2 methods used to connect gas appliances to the household supply.
The first uses a rigid connection, typically used to connect gas hobs.
The second uses a flexible hose, which is used for all other appliances except the hob.
In addition every gas appliance installation requires a method to isolate the appliance from the main household gas supply
Gas hobs are typically connected to the household supply using 15mm rigid copper pipe. They must have a means of isolation so you can turn the gas supply off to the hob. This is achieved by adding a shut off tap to the installation pipework as close to the hob as it possible. There must also be a means of disconnecting the pipework from the hob. This is normally achieved by using a compression joint.
These appliances are normally connected to the household supply using a specifically designed flexible hose that connects to a self sealing bayonet fitting. The bayonet fitting also serves as the isolation device. The siting of the bayonet fitting and the way in which the flexible hose hangs are covered in detail by gas regulations and must be adhered to. Briefly the flexible hose must hang in a "U" shape, (as illustrated in the image below), behind the appliance without touching the floor. It must not foul on any edges or potentially be trapped or be strained when removing the appliance. This is covered in more detail further down the page
Still in use by many manufacturers
There are 2 types of connection One that plugs into a typical plug socket (Or a fused spur equivalent) One that requires a 'Cooker point' The simplest way to explain the 2 methods, is that the more elements you can have on at any one time, the higher the fuse rating and thickness of cable you will require. For example, a double electric oven (2 doors) can have the oven and the grill on at the same time. This would take out a 13 amp fuse, which is the highest fuse rating you can have in a plug socket. So we need a method that allows a higher fuse rating connection. This is accomplished by using a cooker point which is normally protected by a 32 amp fuse