Thanks for letting me know av topped up with brake fluid. It was low got some brake fluid from asda, enjoy your evening my regards Phil
As a general rule,
the brake fluid is in a "sealed-system", almost like 2 x syringes jointed together, as you squeeze one the other fills,
when the brake pads wear out, you replace them with thicker ones, and so squeeze the fluid back, up to the reservoir.
that's the basic theory ..but in modern ABS systems,
It's advised to open the caliper bleed screw, and squeeze(rewind) the piston back, then close the bleed screw, and then top-up the reservoir
whenever I find "missing fluid", I always:
1, check for leaks, ( it's like a light oil.. so you soon see it,
)
2, Inspect brake friction material ( could be completely worn out..!!)