Hi Vicki
As much as I hate to say so, I've had a look at the 1841 and 1851 & I do think they're the same family surname NUTT - and the 1841 occupation for John being
Plasterer, not Porter

which compares to the 1851 occupation - my transcripts:
1841: HO107 / Piece 681/ Book: 6 / Folio: 25 / Page: 46
St Pancras, Middlesex
John NUTT?? 35, Plasterer - N
Thomas NUTT?? 11 - N
Margaret NUTT 33 - N
They are in the same dwelling (perhaps as lodgers) as the family of George THORP, a Painter, and his family. The surname is very unclear, but seems to be 4 letters long and more like NUTT than MOTT to me

HO107 /Piece: 1533/ Folio: 312/ Page: 3
St James, Holywell, Shoreditch, Middlesex
John C NUTT 44, Plasterer & Moulder, b Kingston Surrey
Wife: Margaret NUTT 40, b Whitby Yorkshire
Son: Thomas W NUTT 20, b Whitby Yorkshire
There is an extracted IGI entry for a Thomas William NUTT born 1830 Whitby Yorkshire to parents:
John NUTT and Margaret.
Cheers
AMBLY