Suspecting this is a weed, but it has got quite hefty roots!
Ground elder. A pernicious weed. Nuke it with glyphosate then wait until it has completely died before pulling it up to allow time for the weedkiller to go down to the roots. It will likely re-grow but there will be much less of it - treat each bit the comes up again and eventually you will be rid of it, unless it is coming in from another garden (like mine, from neighbours who do nothing to their garden but cut the grass once a year! )
Don't just try to dig out the roots as they easily break and you end up with more and the roots can go down a very long way.