Guindilla peppers
From Cookipedia
Guindilla peppers are Spanish chillies, often from the Basque Country. They are medium hot with a sweet flavour and in the UK are sold green (pickled) and red (dried). They are long and narrow with a slight curve.
UK suppliers
The pickled, green ones can be obtained in the UK from Delicioso.co.uk and dried red ones from Brindisa.