I purchased one of these English chiming mantel clocks on Ebay. When it arrived in the post I wound up the mechanism, attached the pendulum, set the clock on a level surface and gently set the pendulum swinging from side to side. I soon discovered that it would only tick for a short while before coming to a halt.
A bit of googling led me to this Ebay guide: Set Up Instructions for 20th Century Mechanical Clocks
Instruction number 7 helped me to sort out my problem. Pushing the suspension arm very gently against slight resistance adjusted the set up so that the clock would tick-tock away quite happily. You just have to try it on one side or the other by trial and error until success is achieved.
This Q&A from the AllExperts site explains it well:
I have a Smiths Enfield striking clock with 2 keyholes. Since I first bought it I have had to add some packing under the one side to keep the clock ticking. However, if the clock is standing on a level worktop it will stop the ticking movement within 20 seconds and grind to a stop. But if one side is raised approximately 1cm then the clock won't stop ticking. Is there any way I can get the clock to work on a level worktop without needing to pack paper under one side.
Your clock is "out of beat". In order to correct this, push the pendulum lightly toward the side you have to raise. It will have a certain number of degrees of "free swing". Beyond that, it can be made to move by a friction tight arrangement. When you push it beyond the free swing area, you are changing the beat. Do it just a tiny bit at a time until the tick-tock sound is even when the clock is sitting level. If you overshoot, just do the same in the opposite direction. If you have trouble getting it just right, most repairmen charge very little or nothing at all to make this adjustment. It does take a bit of patience.