It filtered through that returning delegate suggested company could be tardy with first delivery (10)
I believe the answer is:
percolated
'it filtered' is the definition.
The definition suggests a singular noun but the answer is not.
'through that returning delegate suggested company could be tardy with first delivery' is the wordplay.
I cannot quite see how this works, but
'through' could be 'per' ('per' can mean through or by means of) and 'per' is present in the answer.
'company' could be 'co' (abbreviation) and 'co' is located in the answer.
'tardy' could be 'late' (synonyms) and 'late' is present in the answer.
'first delivery' could be 'd' (1st letter of 'delivery') and 'd' is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?