Relating to the above post, national archives have four documents available. You can find their opening hours by navigating their site.
Alternatively there is this link too
http://www.ourwelwyngardencity.org.u...-radio-company
Or failing that contact your local city library to see if they can locate anything. Or another try would be any radio or communication museums . A TV and radio museum I recently visited was called Montecute radio museum. It's in Devon/ Dorset area.