I believe this could be Thomas W in the 1871 census .... age is a bit out (not unusual) but area in which enumerated and occupation seem good.
1871 - RG10/896; Folio: 28; Page: 47 - Northfleet / Gravesend
22, Upper Percy Stboarding with the Popletts ......
Thomas Wickenden 30 Single Boarder Farm Labourer born Kent, Brasted
(I think his PoB of Gravesend in the 1881 was 'for convenience' )
Also noticed that in 1891 (Thornton Heath) his YoB was given as 1840 too - altho sadly, PoB was 'not known'
Its possible to trace this man back to 1851 where he is [step]son of a William Inkpen, and there are Wickenden stepkids in the family ..... you could try and see if he's with the mother Susannah (theres an Inkpen / Wickenden marriage at the right time frame in the SevenOaks District) ... as Tho Wick* back in the 1841 and it might show his father.
Leave it to you as you have access to Ancestry

Added:
Have you verified Mary's maiden name on one of the kids birth Certs ?