An example of Amber found in situ in the cliff section on the North Coast of Sheppey by Danny Hogburn Oct. 2013
 
International Summit Forum of Amber, 2013: Invited Presentation
English amber
Ed A. Jarzembowski
There is another native Eocene amber in England called Highgate copalite, found in the London Clay Formation during excavation in the eighteenth-nineteenth centuries on what was the outskirts of London. It is of early Eocene (Ypresian) age like Fushun amber, but unlike the latter, it's thought to be of angiosperm (flowering plant) and not gymnosperm origin (although even a pine source has been suggested based on gas chromatography-mass spectrometry analysis!) The recently discovered Oise amber in nearby France is of comparable age and also of angiosperm origin, but from a different family (Fabaceae and not Burseraceae). X-ray diffraction analysis suggests that copalite resembles glessite, another (but uncommon) Baltic amber mineral species, whose exact plant origins have also proved controversial. No inclusions have been reported in Highgate copalite, but it should be looked out for in coastal outcrops of the London Clay in South East England (in the provincial counties of Kent and Sussex). ...'

 

German glessite - one of the rarer Eocene Baltic ambers - very similar to Danny's specimen

 
A small specimen of the original Highgate amber from its discovery in 1811. The image includes the original specimen label
For further reading click here for a PDF of oldest account of Highgate amber
 

The nature and fate of natural resins in the Geoshere III.* Re-evaluation of the structure and composition of Highgate Copalite and Glessite.

By Anderson & Botto 1992. To access the PDF, click Here

 
My thanks to Dr Ed A. Jarzembowski For his help with providing a background to this page.
and to Danny hogburn for providing images of the specimen