1. Gently place the samphire in a bowl of water and leave to rest. Any sand will drop to the end of the bowl.

2. Boil the potatoes in water till just cooked. Be careful not to overcook them as you want them to stay firm. Leave to cool slightly before cutting into thick slices.

3. Place the samphire into a pot of boiling water for 30 seconds then remove right away and tip into a sieve, and run cold water over it to stop it cooking.

4. Heat two tablespoons of butter in a wide frying pan. Add the potatoes and fry till crisp and golden. Add the sliced radish and fry for a minute.

5. Meanwhile turn the grill to high and lay a sheet of tin foil over the grill tray. Place it under the heat to get quite hot. Brush it with a little olive oil then lay the mackerel fillets, skin side down, on the foil. Spread the mustard over the fillets and grill for 10-12 minutes, until thoroughly cooked.

6. Add the samphire to the potatoes along with a little more butter. Stir so that the samphire and radish are coated in the butter. No need to season with salt as the samphire is so salty.

7. Divide the potato and samphire among four plates, top with the mackerel and serve with a wedge of lemon.