I luvs a mystery but not having to figure out what it is first!
So we have in Mar Q 1891
Spouge Annie Mansfield 7b 86
Lloyd George Thomas Mansfield 7b 85
and he seems to be the one mistranscribed.
And in 1901 they are Lloyd, but their son was registered as Johnson, parents Thomas Johnson and Annie Spouge.
So it looks like George Thomas Lloyd was altering his identity for a bit. He may even have deserted after the conviction.
Problems with the military are very common reasons for name-shifting.
My gr-grfather on my mum's side unilaterally left the military after 5 years in India, about 1878, and changed his surname permanently -- married under the fake name in England, had kids under it in England and Australia, died under it in Canada. All his kids, and his sons' kids including my mum, and their sons' kids, and so on down, have a fake name.
My grandfather on my dad's side was thrown out of the military at the age of 16, around 1910, for dealing in stolen goods, and promptly changed his given names slightly and re-enrolled in the same regiment, and was in the army under the fake name all through WWI and until about 1925, when he came to Canada and went back to his own name (and apparently required that the British government reissue his medals under his real name!).
Indecency on highway -- he was probably drunk and couldn't find a loo! But punishments were harsh for the lower ranks in those days. And having a black mark on his military record could have made life in the civilian world difficult. So name changing was common.
-- edit -- I was confused -- this was a simple criminal offence in 1894, not having to do with the military -- ? I couldn't identify his WWI records.George Thomas seems to have gotten over his concern by 1900 when his other son was born:
LLOYD Richard Chesterfield 7b 755
Why Johnson? would be the question. Probably no reason: it's a common name that would not make him stand out. I wonder whether it was a joking reference to his 1894 offence.
It's interesting though that you say Harry was born in 1897, but the birth was registered in the april-may-june quarter of 1898. George Thomas may have been still apprehensive and put off registering the birth. I am pretty sure that my gr-grfather who left the army c1878 simply didn't register the birth of his first child after he married in the early 1880s, under any name at all.
... Although - there were two Harry Johnson births registered in Dec quarter 1896, and a Harry Louis Johnson in June quarter 1896 ... just wondering since Harry is shown as a full 4 yrs old in 1901 (and matching age in 1911).
I also wondered whether George Thomas and Annie might have had other children registered as Johnson who didn't survive to 1901 -- that could help date the period of the fake name. There were quite a few Johnsons who were born and died in infancy in the mid-1890s in Mansfield, however.