Do not ever rely on this sort of safety mechanism. There are also systems in use that rely on axle counters and bookkeeping - basically, on each block they count the incoming and the outgoing axles. When your draisine now is either too lightweight to trigger an axle counter or you set it on the rails in the middle of a block, the ops central won't know you are there.
Even simpler, there are systems that use a physical token.
To proceed into a section of track, the train driver/guard must physically possess an object, typically handed over at a station just before the section, and returned just after.
While the UK has indeed stuck to almost exclusively using track circuits for a very long time [1], within the last two decades axle counters have become much more common.
[1] With some exceptions – the Severn Tunnel e.g. was switched to axle counters already in 1987 because track circuits proved too unreliable within the (wet) environment of the tunnel.
