Found this stuff PICCIE
It's made by Tetrasyl but marketed under 'Carplan'. And it's fantastic! I have tried so many products so as to try and avoid the toothbrush scrub. And till now nothing really did what it said.
You literally pour a bit into the supplied cup (actually an aerosol lid!) then take the brush, which is rather like a shaving brush. And just lather it up on wheels - no scrubbing at all! All that burnt on brown brake dust just literally dissolves. Even Renault couldn't get alloys back to new when they valet it, this stuff did!
If you see my wheels HERE you'll know why they're a pig to clean.
Check before buying though as I dont think this is suitable for bare ally, only laquered.