I have been informed that this may well be a Great Northern Railway underslung block bell. Thank you for your interest.
Another opinion, which I hope you all find helpful: “this may be a repeater bell as installed at signal protected level crossings with locally operated signals to give the crossing keeper a warning of trains. Alternately it could be what we call an overland bell that is connected between a advanced signal box and a junction signal box to enable an early warning of trains for a particular route to be given.”