The first part is a battery terminal. The second part is a bomb steady from a light series bomb carrier (a small type of bomb rack). There’s a pic here on a site that strangely enough deals with Blenheims: http://users.cyberone.com.au/clardo/blenheim_armament.html.
That’s a connector for the armourment system – it’s the bit that stays in the aircraft. The Whitley carried 16 of them. I have a lot already – gave up keeping track a while ago. Sometimes it’s easy to drown in the details :p