You can legally obtain a number of hand held scanners that detect and pinpoint electronic espionage devices (bugs) in your premises.

Furthermore, some such devices can be remote triggered and switched on and off and therefor you'll have to do regular sweeps.

The problem for you is that only an amateur would use such devices. Its quite easy for the intelligence services to tap your calls external to the property as part of a legitmate investigation.

Its also possible to bounce a laser off your windows and record sounds from inside back along the stream.

Also worth noting is that resources are limited, and no ones going to spy on you unless your demeeded a threat... eg you are beleived to be involved in espionage, terrorism, sabotage, actions likely or intended to overthrow or undermine parliamentary democracy by political, industrial or violent means, or have or are involved in groups involved in those activities.

heres a tip... dont get involved in groups that want to use or condone violence as a tool of protest.