Home made is best! Just add a couple of dessertspoons of salad cream to six tablespoons of mayonnaise, then add chopped gherkins and capers (rinse the capers well or use the smaller less salty ones). Coarsely chopped gherkins and capers look good. Add chopped basil or parsley for colour. The amounts of capers, gherkins and herbs are up to you, but it looks good if it's a chunky-looking sauce, more solid than liquid.
This sauce is great served in individual bowls.