I've just seen that the ITN Archive system has been upgraded considerably and is now at www.ITNsource.com
A quick search for motor racing 1897-1964 gave some 3,200 results. Whilst many are the existing Pathe & Movietone, there's more detail on the Reuters archive, including Paramount and British Gaumont. Some previews are available, probably pre-existing Pathe/Movitone, but I understand the plan is to extend digitisation and there appears to be much more detail on other clips. There's also a facility to create a personal project file.
Either way, the interface has been improved significantly, and it's probably worth bookmarking for future use.