For the Marie Rose sauce, mix the mayo, ketchup and Worcestershire sauce in a bowl. Add a good squeeze of lemon juice and a splash of brandy (if using), then have a taste and season to perfection with sea salt and black pepper. (See tip for brown crab meat below.)
Click off any tatty outer leaves from the lettuce, then trim and finely shred. Slice the cucumber and radishes into super-thin rounds with a mandolin, if you have one (use the guard!). Halve, peel and destone the avocado, then finely slice.
Mix the crabmeat with the mayo.
To serve, arrange a small pile of lettuce in the middle of each plate, top with a few slices of avocado, then arrange the cucumber and radish around the edge, overlapping slightly.
Divide the crab between the plates and drizzle over a little Marie Rose sauce. Scatter over the cress and micro herbs, then add a dusting of cayenne pepper and a wedge of lemon. Delicious served with brown bread and butter.
If you're cooking your own crab, fold a little brown meat through the Marie Rose sauce to really make the flavours sing.