The label is the operating instruction
HSE guidance says pesticide products should be used as instructed on the label. Professional-use products require appropriate training and should not be used by untrained householders.
Never mix products or increase concentration in an attempt to make a treatment stronger.
Residual action needs placement
Residual products are intended to affect insects that contact a treated placement after application. Cleaning, covering or applying to the wrong surface can change performance or safety.
Occupants need written re-entry and cleaning instructions.
Resistance changes the plan
Bed bug populations have documented resistance to some insecticide classes. This is one reason credible programmes combine inspection, physical methods, carefully selected products and monitoring.
A surviving insect does not tell you the exact resistance mechanism, but repeated unsupervised spraying can complicate assessment.
Sources and further checks
Open the source before acting on information that may change, including council services, prices, tenancy rules and product labels.