Unfortunately Sundora has been bought up by Whitworth and they have discontinued the whole candied peel line. Is there any equivalent for sale that you know of? Sainsbury and Waitrose no longer sell it as it is no longer available from the manufacturer.
Nigella uses whole candied peel in her version of Black Cake (from Domestic Goddess) as this peel can be cut into larger pieces than the usual chopped mixed peel and often has a better flavour and texture. Unfortunately it does seem to have been removed from widespread distibution.
However the whole peel is available on-line, sometimes described as crystallised peel. Melbury & Appleton sell whole candied/crystallised orange and lemon peel on their website. A website called Buy Wholefoods Online also sell mixed whole peel, plus lemon and orange peels. Their products also seem to be available via Amazon.