This marmalade ... no more than 1.4kg/3lb 1oz. If you have more than this, return the contents to the pan and simmer to reduce the liquid until the correct weight is achieved. Add the warmed sugar ...

Slice the peel finely or coarsely, depending on how you like your marmalade ... soft before the sugar is added, otherwise when the sugar is added it will toughen the peel and no amount of boiling ...