Sounds like the remains of a Pattern 1853 Enfield rifle-musket, with mixed parts (and cut down).

The markings on the top of the barrel are the barrel proof marks, and as described, would be those of the Birmingham Proof House. The 25s were the bore gauge numbers at the Provisional and Definitive (final) proof. The two 25s and the other small markings (crossed scepters) were in Birmingham proofs, not London - the London proofs were different. So it looks like this is a Birmingham barrel with a London lock.

Henry Clive was the barrel maker - one of the Clive family who commonly made barrels for Birmingham guns.

Joseph Bourne was a gunmaker in Birmingham, and this is most likely the firm that actually made this Enfield (not Barnett).