Hi Mark have you got a photo of the area? as it might produce some ideas from members. I found in this situation the deeper the bed the better and to incorporate lots of compost etc first. I can think of several shrubs but cottage garden planting needs better conditions to thrive. My thoughts have been on seeding a wild flower area? which could go with the CG theme.

How about potentillas? Also after enriching the planting area with lots of humus, compost etc, try mixing some water retaining gel crystals into the planting holes. It really does make a big difference to what will survive in those conditions.
Succulent plants such a sedums would be OK and euphorbias might be worth a go.

If the soil is very 'rooty' you might be best sowing hardy annuals, now. Try Nigella, Marigolds, poppies. Anything Mediterranean and herby would succeed too, try Thyme, Origanum, Rosemary. The secret may be to plant very small rooted cuttings in Spring and let them get their roots down. Larger plants would need too much water before they find their own supply. Or try placing pots with more lush plants in. Or would it be a nice sunny spot to mulch with gravel/bark and have a bench on it?