Being purely mechanical, the brakes worked even after having stood for 25 years. However friction in the linkages means that they are not very good at stopping the car!
A vital part of the system is the front brake Bowden cables, fitted only between September 1934 and July 1936 on the Tens, however they can still be repaired (see Parts Suppliers page)
The reason it was not very good at stopping was found to be that the linings were worn right down and there was no adjustment left on the Bowden cables!
The front cables were initially lubricated with Graphited Grease.
Some leaked out of the coils of the flexible cable but a build-up of pressure soon had the grease on the move! However see Jun 05 below - oil is better - it flows easier and in fact I subsequently blew apart one of the turns of the outer casing with the pressure I needed to force grease down the cable.
All seemed well, but a niggling feeling made me re-check the nearside brake cable and sure enough, several strands were parted under all the grease.
Oil nipples seem to be no longer available so I used a grease nipple and used SAE140 oil in my grease gun. (but see better solution below)
Shock, horror - the offside brake cable that I had thought "good" also had a number of broken strands.
It was very stiff to move; I only took it off to wash out the grease and oil it!
So off down to the local dealer and got me yet another cable!
a final point - it has been recommended that the Bowden brake cables should be oiled rather than greased as the oil will move back onto the pressure points. Although it is possible to use a grease gun for oil, it can be messy.
Proper oil guns are not easy to find and I eventually bought an Abnox-Wanner 30960. It took a while to get rid of the grease but things got easier once the grease had been diluted by the oil and pushed out.