Strange new grass growing up through plants

There is a strange grass that has invaded by garden. It has fibrous woody-like underground runners and is quite proliferous. The grass it produces is lovely but out of place among the established lavender and hydrangeas and it is impossible to pull. I have to dig down about 6 inches into the soil and under the plants to remove these runners. What is it? It is new this year – could it have come in with a hydrangea planted early autumn? Thanks very much.Desperate in Carrick!