Possible Clues:

• Substance melted and stamped on official documents
• It is used for closing letters, documents etc
• It's given the impression salt-water fish grow larger
• Preparation for documents once Spooner's transporting luggage
• I used to stamp letter, finishing off with a kiss
• Finally deciding to grow ... cabbages next, of many things to discuss
• Resinous substance reportedly hits roof first
• London borough (West) cuts instrument for joiner
• It is heated and dripped onto documents
• Old-style letter closer