Mac,
None of those things you mention provide any proof that the rifle was put together in Britain.

The proof is in the proofs!

If the rifle does not have a full set of correct British proof marks then it is highly unlikely that it was ever put together in Manchester.

The true Manchester Whitworths do have those correct proofs.

Crown over V could have been put there by anyone.
The poms have not used that mark for a long time.