Clerkenwell, London.
I picked a single flower bud and opened it, damaging it slightly in the process. This flower then measured 4cms across.
Clerkenwell Japanese Bitter Orange plant.
Poncirus trifoliata bud
Clerkenwell Poncirus flower
Poncirus at RSPB, Sandy
Poncirus at RSPB
Poncirus buds detail
Click here for location details of these and other Poncirus trifoliata plants.
This plant, about 2m. (6ft.) tall, is in the garden of the RSPB headquarters near Sandy.  Photos taken 15th April 2005. 
Page updated 12th November 2006
Eltham Palace Poncirus trifoliata
Eltham Palace, London.
An English Heritage property, much of it dating from the 1930's, when it was owned by the Courtauld family.
The Poncirus is an unusually tall, single-trunked specimen which I guess could have been planted at that time. It is leaning over at an angle and has growth only on one side. The tree has few spines - an indication of an old plant - but, in July, plenty of small, unripe fruits.
Photographed July 2005.
Sandy, Bedfordshire, England.
Cannizaro Park, London borough of Merton
Flowers still just closed, 25th April 2001.
Cannizaro Park Poncirus fruit close-up
Poncirus trifoliata in Cannizaro Park
Although this shrub was not a very fruitful specimen, the fruits were notable for their nobbly surface - somewhat reminiscent of the peel of the Thai Lime. Internally, the fruits were also unusual, having very dry flesh and tiny  seeds. These were probably not fertile, although I have planted a few to see whether any may germinate.
If you visit Cannizaro Park, don't miss the olive tree grove in the Italian garden at the bottom of the main lawn. Who said olives can't be grown in England?