This looks remarkably like a flowering stem on Acanthus mollis - but there are no leaves. Have you had this plant in the garden before, and thought you'd dug it out?
Otherwise, probably one of the Lathraeas, maybe L. squamaria, seems a bit tall for L. clandestina. Lathraeas are parasitic/symbiotic on roots and are usually produced in forested areas, but don't cause any harm to the trees. Common name is Broomrape or toothwort. Be interesting to see how it develops!
UPDATE: Been checking, but all the non agricultural information is to do with getting the stuff to grow, not trying to get rid of it, particularly L. clandestina. I doubt you'll get rid of it altogether, as its parasitic on woody roots - most of its activity is underground, but you can try glyphosate if you want, or just dig out the flowering stems as much as possible when you see them. This plant can be a huge problem in agriculture, but not so much in our gardens.
UPDATE 2: Yes, its actually Orobanche, probably O. purpurea, not Lathraea. Even so, it's not really an issue, its classed as a rare Wildflower. This one usually grows in association with Achillea millefolium, if it grows at all. Can be annual or possibly perennial, likes dryish, light soil.