Bexley Archive probably has the best record of Gypsy and Traveller histories. Bromley Local Studies Archive also holds a very few pictures, and it may be worth searching archives in the Mitcham area, where there was a regular fair for many years.
The Old Bailey Online chronicles how Gypsies and Travellers who were tried in London from the 18th century onwards. The site doesn't list all the court cases in one place, it suggests helpful search strategies and terms used to describe Travelling people.
Much of the Museum of London is closed at the moment for rebuilding, but a sample of their Traveller objects are on this website. The Museum of Childhood also holds oral histories of young Traveller lives: Tracie Giles recalls the discrimination she faced at school. Their website also looks at how Gypsies arrived in the East End.
Currently archived, but often on display is the National Portrait Gallery's image of Thomas Bamfylde Carew who ran away with the gypsies and gained some stature in the community.
Gypsies in War
The only permanent exhibition in London that touches on Traveller lives is a very dark one. The Imperial War Museum's disturbing Holocaust exhibition describes how Gypsies were amongst those earmarked for destruction by the Nazis and the increased harrasment of the communities before being taken to the death camps. Thomas Acton writes more about the genocide of Gypsy cultures .
V&A
The V&A have a number of photographs and images relating to 19th century Gypsy lives in England. Traditional aspects of Gypsy life were fashionable in 19th century Britain, leading to the founding of the Gypsy Lore Society, which included painters such as Augustus John. The collection also includes pictures of leading Gypsy figures of the time such as Granny Buckland and Bampfylde Moore Carew. These pictures aren't on display in the museum, but you can see the originals by going to the Prints and Drawings Room at the top of the building, and ordering the images that you'd like to see. You do not need an appointment, and images will generally be put into your hands within 15minutes or so.
The V&A also has many pictures by Josef Koudelka who took photos of life in his native Czechislovakia - which include pictures of Gypsy life.
Documenting the present
The V&A is probably the museum that's done the most to explore Gypsy and Traveller culture - and it has housed a few photography and exhibition projects in the past created in collaboration with Travellers. But generally, the relationship between museums and Travellers has not been a strong one and the highly politicised story of modern Traveller lives is notable by its absence.
Knight is emphatic about the rawness of the issues:
'It has been a cultural genocide. In 1995 there was a duty placed on local authorities to identify land for travellers to buy - this was after 77% of land was taken from us. This duty was completely ignored - it never happened. Then the problem for travellers was how do you access doctors and schools. It's easy to see how people have become forced into housing.'
On the one hand this history month is about increased organisation and confidence. But this is not then a community looking back from a more-comfortable present to an exciting past. Traveller identities have always been marginalised and from time to time have been punishable by death. Now they seem most at risk from a set of laws that leave the Travellers apparently unharmed but deftly remove the means for a nomadic life.
This month is carefully framed around history, not the politics. But underlying it is the question of whether an appreciation of the Travelling past will help prevent the smothering of a travelling future.