Place a medium frying pan on a low heat. Add the mustard seeds, peppercorns and coriander seeds. Toast for a couple of minutes then tip into a bowl.
Add all of the pickling ingredients into a saucepan. Bring the mixture to the boil cook for 2-3 minutes. Allow to cool. Fill a sterilised jar with the cooled eggs and cucumber slices then pour over the cooled mixture.
Pop the lid on tightly and leave in a cool, dry place for around 2 weeks to 1 month. Once opened, keep in the fridge and consume within a week.