Can anyone help date this photograph?

[B17_Fan]

My grandad recently passed away, and we've started sorting the house out. We found this old locket and have no idea who the people are. I've attached a photo of the younger gentleman, as he has a cap on and it looks like a badge on it. We don't know if it's military, or even if it's a uk uniform. Can anyone help date or identify the badge on the hat?
Many thanks

[jim1]

Although difficult to say he is possibly wearing a high starched collar
typical 1880's/90's.
His cap appears to have a number on it possibly 1216.
Possibly Postal service.
He looks in his 20's.
A lot of possiblies I know but not much to see is there.

[Milliepede]

When was your granddad born?  That might help with what generation the locket might be from
ie a brother or an uncle for example

[Kloumann]

Is the locket hallmarked? You could get a date from that.

[jim1]

Is the locket hallmarked?

As it's rusty it must be plated base metal.

[japeflakes]

No extra info but perhaps easier to see.

[Treetotal]

Could post a photo of the other photo, it might help with a date.
Carol