Most items of uniform supplied by the War Office came issued with General Service buttons. These were the standard military pattern of button with the Royal coat of arms on them and they were used on a wide variety of uniforms over the decades, including the Home Service uniform, tropical uniforms and Service Dress. There were however unique regimental patterns of buttons that can often be seen on surviving garments and in period photographs.
Officially it was Regimental bands who were permitted to wear distinct regimental patterns of button, with one set being issued per band member. It was however common for sets of regimental pattern buttons to be purchased either centrally through regimental funds, or individually by the soldier, which were then sewn onto uniforms in place of the GS pattern to give a unique regimental distinction to the jacket. Almost every regiment had its own pattern of button and collecting them is a very cheap and fun little sub area of militaria collecting. Here can be seen a selection:

The buttons themselves are made of two pieces of brass. the front half is stamped with the badge itself in a set of dies resulting in a crisp pattern:

This is then cut out and attached to the rear half of the button which contains the wire loop to sew it onto the tunic and has the manufacturer’s details pressed into it:

There are dozens of different buttons to track down, some of the more obscure regiments being very difficult to find. On top of this examples can be found for many colonial units to add another layer of collecting. Buttons tend to be cheaper than cap badges and can often be found in junk boxes for 50p each or less, well worth keeping an eye out for.