A bit of guesswork (having noted that many of the 64th came from Lichfield) brought me to this interesting possibility for George in the 1861 census:
Rotten Row, Lichfield
William Mann 60 labourer, Roscommon
Catherine Mann 56 wife, Ballanlubber
Patrick Mann 17 son, labourer, Roscommon
Bathley (Batholomew?) Mann 13 son, Roscommon
George Mann 10 son, Lichfield
The next household to be enumerated is Frederick Lees, a Drill Sergeant Major
However - those "deserter" records apparently give his birthplace as London