Would someone kindly identify this weed/plant for me.

It is about 18" tall, has leaves very similar to those of a foxglove and
at first sight it could easily be mistaken for a foxglove. Its flowers
are almost identical to those of a Lithodora 'Heavenly Blue'.
http://tinyurl.com/5ganxe
It has woody roots which are fairly deep and clump forming and is very
invasive, particularly by self seeding.

Thanks,
Emrys Davies.