The Eat the Seasons website has been up-dated and now has lots of signs to show imported veg, etc. they are also now including this like salad leaves in their lists too.
broccoli*, carrots, cauliflower, chicory, cucumber, jersey royal new potatoes*, kale, leeks, lettuces & salad leaves, onions, potatoes (maincrop), purple sprouting broccoli*, radishes*, rhubarb*, rocket*, samphire, salsify, spinach*, spring onions*, watercress*, wild nettles*
HERBS, FLOWERS, FUNGHI, NUTS
basil, chervil, chives*, coriander, dill, mushrooms (cultivated), parsley (curly), parsley (flat-leaf), sorrel*