Finely slice the fennel, celeriac, red cabbage, white cabbage, beetroot, onion and carrots and place into a large mixing bowl. Add the fennel seeds and salt. Mix thoroughly, then leave to stand for 20 minutes so the vegetables wilt and cure in the salt.
For the garlic dressing, add the garlic, egg yolks, white wine vinegar, mustard, lemon juice, anchovies and sugar to a food processor and blend until smooth. While the food processor is still running, slowly pour in the vegetable oil in a thin steady stream until the mayonnaise is emulsified. Season with salt and cayenne pepper, to taste. Pass through a fine sieve to make it really smooth. Keep in the fridge until needed.
Rinse the vegetables under cold running water for a couple of minutes. Place in a clean tea towel and squeeze out all of the moisture. Put the vegetables in a clean mixing bowl and add the lemon zest and chopped herbs. Check and add seasoning if required. Fold in as much mayonnaise as you like, you may not need it all. Mix together and serve. The coleslaw will keep in the fridge for up to one week.