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Large leaved plant with small blue flowers close to stem. Very vigorous growth. It is growing in London, United Kingdom in my back garden in semi shade. It first appeared last autumn with large leaves, which died away over winter, but has suddenly shot up over the last month, and is now two foot high and spread, with the small blue flowers having appeared in the last week.
It is Pentaglottis sempervirens (green alkanet), a member of the boaginaceae family (making it a "cousin" of the comfrey from Bamboo's answer (similar leaves), of forget-me-nots (flower!) and borage).
Like all his cousins it has a tendency to spread and self-seed, but is often tolerated to a certain extend because it looks pretty flowering almost year-round, thrives even in shady corners and the flowers are edible, like borage flowers.
It's Symphytum asperum, commonly known as comfrey or rough comfrey or prickly comfrey. Though pretty, it's a pernicious weed, but some people actually buy it for their gardens - make sure you remove any small ones when it seeds itself later, while they're still small and easy to get out. Those which have been established for more than 2 years have very deep roots, but if you like it, keep it - just keep a watch for the inevitable offspring which will arise. If you don't, it'll be everywhere...
When its small, early in the year, its easily mistaken for Foxglove (Digitalis), but if you touch the leaves, you can tell which is which - Foxglove leaves are pleasant to touch, this plant's leaves are not.
UPDATED ANSWER:
My ID was incorrect (thanks to Stephie below) - I read 'London' and glanced at the plant rather than examined it closely. This one is actually Pentaglottis sempervirens, common name Alkanet, just as much of a pain as that previously described, and again, commonly pops up in and around London. All other info remains the same...
It's comfrey. Look up videos on comfrey, I just watched like 10 last night, it all had white or blue flowers. Look up "comfrey identification" and go to videos.
