Peel and finely chop the onions. Peel and thickly slice the carrot. Peel and roughly chop the swede. Slice the roots off the celeriac on a diagonal to slice them off cleanly, then peel the rest and roughly chop the celeriac.
Put a large pan over a medium heat to warm for 2 mins. Add 2 tbsp oil, the onion and some salt and pepper. Cook for 5 mins, stirring now and then, till they slightly soften. Add the chopped carrots, swede and celeriac and cook for another 5 mins, stirirng now and then, till the veg have all started to soften.
Drain and rinse the lentils. Crumble the stoc cube into a heatproof jug and stir in 1 ltr boiling water till the stock cube has dissolved.
Stir in the hot stock and add the lentils. Pop on a lid. Bring to the boil, then turn the heat down and simmer for 15 mins.
While the scouse simmers, peel and roughly chop the potatoes. After 15 mins cooking, add the potatoes to the scouse. Simmer for another 10 mins till the potatoes are almost soft.
Finely slice the leafy greens, discarding any thick stalks or cores. Add them to the scouse and push in with a wooden spoon. Simmer with the lid off for 5 mins to finsih cooking the spuds and just wilt the greens,
Roughly chop the soft green herbs and stir them into the scouse. Taste and add more salt or pepper if you think it needs it. Serve the scouse in warm bowls.