i would suspect providing there is plenty of water available then many ground cover shade plants will be fine. eg ajuga, pachysandra, pulmonaria and dont forget lots of bulbs too.

Thanks for your answer - do you have any further advice please re the additional info in the question?

I mulch mine with acidic compost (80L) to give it a good boost twice a year and this has improved the leaf colour. I dont attempt to grow anything directly underneath because Labs prefer dryer conditions.

I cant say that i have noticed any effect from the seeds on what grows under it. certainly the weeds still grow freely.