It is possible to use the Ordnance Survey Open Data 1 to 250,000 raster maps as a background layer in JOSM. However, the positional accuracy of this scale of map is limited. This could also apply to the StreetView tiles, but they are readily available as a WMS layer, which is probably preferable.
source: OS_OpenData_StreetView when editing OSM was becoming tiresome. Therefore I hacked together a quick sources preset based on one for Spain by user Sanchi. Perhaps this will be useful for others editing OSM in the UK using JOSM.
I have done most of my Open Street Map editing using the free JOSM Editor, as I feel it has a number of advantages over the default, Flash-based, Potlatch editor built into the website. The feature I use most is the various background image layers, but also being able to quickly loading my GPS tracks and support for other plugins are useful too.
Over the past few months I have been getting involved with the OpenStreetMap project — a Wikipedia style map that anyone can edit, and use for whatever they want.