Seems to have stumped everyone here! It looks very familiar though.

Isn't there a list of contents on the seed packet?

No it was just a packet of mixed perennials I bought!
Mystery indeed

it looks like a type of figwort. that's the nearest I can get from wild flowers. its a member of the labiate family going by the leaf/stem and flower shape.

I've just seen Foxglove 'Illumination Pink'. Were the seeds from Thompson & Morgan? I think your best chance of identifying it might be to contact the seed company and ask them what was in the mixture.

The leaf is definitely not a foxglove but does fit figworts.