PS:

The Triton 'filter' is just a small thimble-shaped 'bundle' or
brass-coloured wire held within the 15mm shower inlet fitting. Rather
like a small version of those those stainless steel 'brillo pads' that
you put inside the kettle to attract scale.

Triton charge a fortune for these and I'd like to source an
alternative. However I've no idea what they might be called. Any
suggestions?

Thanks
J^n