Motorist Stores

Here in France feu vert is the obvious alternative, though they appear to be franchises and the inshop range is not quite as wide as Halfords. They seem to be a workshop plus shop so are usually to be found in the light industrial/supermarket/furniture shop ghettos outside a town. Otherwise the big hypermarkets usually have a car section that contains most of the essentials.

Pene Auto is more of a trade counter-type place and seems to have quite a few branches around my part of central-SW France.
There's also FAP - France Auto Pieces - which does tyres, batteries, spares and servicing and seems to have a lot of branches.

Norauto in Belgium too.
Also try Auto5.

Feu Vert is a very expensive franchise operation, as said, the larger French supermarkets usually have a large range of products such as filters, brake pads etc. If you can't find what you need there then the main dealers are the last resort with their rip-off prices.

I forgot to mention in referring to Feu Vert that I went there to buy some car ramps. I got to the cash desk to be told that the price shown was per ramp - do motorcyclists buy single ramps as I can't see any other use for just one and I've never seen anyone else pricing ramps singly rather than the pair! At double the price it was cheaper to leave the ramps at the cash desk and go elsewhere.