What is this and do i need it?

[drunkpig]

Hello all. This unidentified part is leaking so need to replace but have no idea what it is. Its on the mains in just after the stopcock . grateful for any help Ta Paul

 

[JCplumb]

I'm thinking old water softener or hammer arrestor.

 

[PETE 123]

Magnetic scale reducer.

 

[king of pipes]

Its a old limescale reducer you will probably have mixed advice i would advise a all metal replacement unit as below. Kop

 

[drunkpig]

Thank you all. hopefully I can change it without destroying my bathroom.👍