Throw them away, too much hassle to clean.
Fire will get the hammerite off, but it'll burn the bristles too so...
3 for 99p brushes and discard after use
In my experience the most recent recipe Hammerite cleans up OK with white spirit, unlike the old stuff.
I bought the 750ml size for £19.99 from Amazon.£10 for a 250ml
I agree. But that said I do wash brushes if the paint is water based, like house paint, including, thankfully, modern woodwork paint.
If it needs industrial solvents to clean the brush, then I'd argue it's less bad to bin the brush