Can find no trace of Henry Walter Whitfield in any immigration records.
A Henry W. Whitfield bc.1888/9 d.Mar.qtr.1953 Westminster, London
There is only one Henry W. born this period in England and this is your Henry Walter.
A Henry W. Whitfield married in 1911 Mar.qtr. Pancras, London to either an Edith Chapple or Catherine Comini. The other groom is a James Iseppi and I suspect the 2 with the Italian sounding names married each other.
There are 2 children born Whitfield, mothers maiden name Chapple and I can't find another Whitfield married to a Chapple so parents could well be Henry W. Whitfield and Edith Chapple:
James H. Whitfield, mmn Chapple born Sept.qtr.1912 Exeter, Devon
Florence L. Whitfield, mmn Chapple born Sept.qtr.1917 Willesden, London (wrongly shown as in Oxfordshire on Ancestry)
A James H. Whitfield married in Paddington in 1937
A Florence L. Whitfield married in Willesden in 1935.
An Edith Whitfield b.1888 died 1960 Paddington
So, the pieces seem to fit but the only way to know if this is the correct Henry W. Whitfield is by getting the 1911 marriage certificate.
I note an Edith Chapple was born in Liverpool in 1888 - if, as you suggest, he enlisted before the war did Edith move South to marry him? Was it his career which took them to Devon where 1st child born and then back to London? All conjecture at this stage and only marriage details can confirm if the above findings are correct.
Annette