If anyone can answer this it will be MN. On going up t' town this w/e. I passed a church with an 8ft shrub outside it. Said shrub had a cream/greeny flower - 4 petals - in quite a geometric shape (kite..ish). The plant was close to the edge (ignore pavement) of the A3 somewhere between Clapham and the Royal Hospital (going that way it was on the right). For the life of me I cannot find this in any of my books and no-one in RL recognises my description - can MN solve the mystery ??