Singing is an athletic activity as well as a musical one. Good health will help retain your voice. Also good vocal health (learning to use it in such a way that you don't abuse it).
Diet and judicious exercise is an important component. Getting enough rest has a restorative affect.
Get a good vocal teacher who has a good singing voice and can help you keep what you have.
Pubs are not the best place to keep a voice in good condition. Smoke hurts you.
Shouting or yelling or excessive belting can damage your cords as well.
Take it easy on yourself by not pushing too hard and get some vocal help. You will have to scout around to find a good teacher but it's really worth it if you want to keep your voice.