I checked the age again - Ancestry has transcribed it 27 so dob 1844 and name Marvill (I used Findmypast to find it originally) - there is enumerators mark through the age so I may be wrong about it being 37.
Maybe get second opinion from other listers?
Maybe there could be two Augustus MERRILL’s 
1851c HO107/1472 page 1
Mary MERRIL Head Wid. 70 Liv…? Private          Norwich, Norfolk
Marion              dau    wid  37  milliner                          “               “
Elizth                dau       u    27  dressmaker ?                   “             “
Augustus           son              7                                    Middlx, London (transcribed as son of Elizabeth Merrill)
1861 RG9/349/43/31
Mary MERRILL Head Wid 46 Norwich, Norfolk
Augustus W          son           17 Holborn St. Andrews, Middlx
1871 RG10/653/80/19transcribed
Augustus William MARVILL 27
Ellen Marin                              26
Marian Louisa                          14
Elizabeth Emma                         7 mths
Original 1871 census age looks like 37 for Augustus
Augustus William MERRILL 37 Middlx, city oflondon
Ellen Maria                              26 Westminster
Marian Louisa                            4 Surrey Lambeth
Elizabeth Emma                          7 mths      “