Not a problem, mow them off. There is no treatment which will stop them permanently, but they only appear for a few days about now.

That is usually the case but one of my customer's lawns had a 10 footy diameter "fairy ring" of mushrooms which kept on erupting with mushrooms every week for 6 weeks last year (? possibly caused by the very long period of wet weather last year) This year I've seen only one mushroom on that lawn

They don't cause any problems to the lawn, in fact you could say that you are lucky because it's usually a sign of a healthy lawn. If you're 100% sure that they are edible mushrooms, then you could always eat them ;o)

You should be so lucky! NB there are some that look like edible field mushrooms in every respect except that they bruise bright yellow - don't eat those!