chudford wrote:

What is the best way to clean them without damaging the alloys or the
tyres?

Cillit Bang, but wash it off quickly and thoroughly. You can buy
expensive compounds such as "Wonder Wheels" to do the job, but
chemically it's very similar to Cillit Bang, a mixture of sulphamic
acid, a detergent and a lot of water. And acid cleaner is needed to get
the baked-on brake dust off the wheels. Once you have them clean, don't
use it again, regularly clean the wheels to keep them in good condition.

Over use of an acid cleaner will damage alloys.