Judith in France wrote:

Smell them, if they smell of honey, then there is probably a rotting
tree stump underneath. I had those in the UK, it didn't hurt the lawn
and I'm told you can eat honey fungus?

I've removed & disposed of them now as I needed/wanted a final cut to
the lawn, and yes, there is an old tree root underneath where they were
but it's a bit too big to remove

Thanks for all the answers and I'll not overly worry if they re-occur.

--
Chris