Just come over from the Armed Forces board

...
Now for the first pic...
I would say that the pic dates from around 1910ish (the collar and cut of the jacket).
I would also punt that he is from one of the steamship companies, such as P&O or Ellerman Lines (Merchant Navy Class - Southern Railway's named a series of engines after a slack handful.. ) or something of that ilk.
I've tried to look at some but haven't found it ...yet!
The Merchant navy had just a badge with MR surmounted by a crown within a rope type thing...
Perhaps he's a steward or something....
The second pic...They are
NOT No4 rifles they are
No1 MkIII. SMLE

L1A1 are SLRs 7.62mm not Lee Enfields....

I would punt that there is NO chance that his pic is post WW2....

They are wearing 1908 ptn webbing in the first style as they have not been altered for trench warfare. The next style came in in 1937. The Navy did have some weirder bits to their webbing, but this pic is deffo PRE WW2...
Only during wartime did the cap tallys say "HMS" rather than a ships name. that notwithstanding...I have seen some WW1 pics with named tallys on...and with white topped caps...summer wear
It was not unknown for someone in civvy shipping to transfer to the Royal Navy...given my presumed date of the first, he may have transferred during WW1, and then stayed in...

Have you searched for a medal card yet, or perhaps his Naval records???
Another thing...several of the cap tally bows are towards the front...This is done in times of celebration...