What happens to the ashes ?

I am interested to know what actually happens to a person’s ashes, if the family choose not to collect them.

I am primarily refering to the ashes left behind after a crematorium service, and the stories heard about Aunty X carrying her deceased husbands ashes with her for ever more…
What happens to the ashes that don’t get put in an urn and placed in a handbag / on a mantelpiece / in a memory box, etc.

I truly hope this question does not offend, but I am interested and can not find an answer.

Here in the UK, the ashes are often scattered in the garden of remembrance (the crematorium grounds) - the rose bushes always look very strong and healthy.