This grower is fairly sure of this plant identification.
Welsh yellow flowered poppy. Will self-seed.
Meconopsis cambrica (Welsh poppy). This is a compact clump of bright green foliage. The flower stems are strong and hold the prickly buds which will open to reveal solitary blooms of orange or yellow blossoms.
They will need a moist but not over-wet, lime-free soil with plenty of humus and a cool site in part or full shade with shelter from strong winds. You can propagate from seed in late summer. They are poisonous and allergenic.
Walls, rock garden, shade, border, wildflower/meadow