The duties
Is calibration a legal requirement in the UK?
Updated
No single UK law says every instrument must be calibrated. Duties attach to particular uses: equipment that weighs or measures for trade, control measures under COSHH, and work equipment whose safety depends on how it is installed or how it wears.
Weighing equipment used for trade
Business Companion, the trading standards guidance service, says weighing equipment used for legal purposes must be accurate and made to an approved type approval or examination certificate, and is either passed as fit for use for trade by an inspector of weights and measures or approved verifier, or qualified for legal use by an approved manufacturer or body.
Source: Business Companion (CTSI): weighing equipment for legal use
The law behind it is the Weights and Measures Act 1985 and the Non-automatic Weighing Instruments Regulations 2016.
Source: Non-automatic Weighing Instruments Regulations 2016
Local exhaust ventilation under COSHH
HSE says COSHH requires control measures to be maintained and thoroughly examined and tested at set intervals, and that LEV must be thoroughly examined and tested at least every 14 months.
Source: HSE: maintenance, examination and testing of LEV
HSE's LEV guidance says to keep all records for at least five years.
Source: HSE g406: LEV examination (PDF)
Work equipment under PUWER
Regulation 6 of the Provision and Use of Work Equipment Regulations 1998 requires an employer to have work equipment inspected where its safety depends on the installation conditions, and to have equipment exposed to conditions causing deterioration inspected at suitable intervals.
Source: PUWER 1998 regulation 6 (inspection)
Everything else
Beyond these duties, calibration is usually asked for by a customer, a contract or a quality system rather than by statute. This page is information, not legal advice.