Telford tattooist at last has covered over mark (6)
I believe the answer is:
thomas
'telford' is the definition.
(engineer Thomas Telford, 1757-1834)
'tattooist at last has covered over mark' is the wordplay.
'at last' indicates one should take the final letters.
'covered' is an insertion indicator.
'over' becomes 'o' (cricket abbreviation).
'mark' becomes 'm'.
The final letter of 'tattooist' is 't'.
'o'+'m'='om'
'has' placed around 'om' is 'homas'.
't'+'homas'='THOMAS'
(Other definitions for thomas that I've seen before include "Dylan --; -- Edison" , "The Blue Boy painter, d. 1788" , "Doubting disciple" , "The doubting one" , "Doubting apostle" .)