An olive tree in the heart of Clerkenwell

We popped up to London for the day to let in an electrician who is repairing something in our flat.  I went for a walk and found this olive tree which is only about a quarter of a mile away from the flat but I've never noticed it before.  It is in the garden of the Order of St.John (as in St.John's Ambulance).  The garden was established in the 1950s on the site of St.John's Church that was largely destroyed by an incendiary bomb in WW2.  The wall in the background is part of what remains from the 1300s church.  It's a Garden of Remembrance and is full of medicinal herbs that were used in the Order's medieval hospitals.