John
I had the same issue last weekend. It seems almost overnight that my lawn grew 100 odd toadstools/mushrooms in 20ish clumps. I think that the weather conmditions being mild yet damp over the last few weeks has providfed the ideal conditions for them to grow, as last year I had none but the year before some.
I just tried to pick them out the best I could then scarified the lawn and forked it to try and help drainage as much as possible. They are so unsightly and not in the least magic! I doubt that they wont come back but at least for now it looks better.