I called H&H on a gun (when they had an office in NYC). They read me specs over the phone. Purdey's may give you the barrel length without charging. Until you send the email, you'll never know.

It would be interesting to know if Purdey built a 25" gun. H&H built came out with the Brevis model in the 30's to get in the lightweight fad. The barrel length was 26" or 26.5".