# The Road Vehicles (Construction and Use) Regulations 1986, Paragraph 10

Extent: E+W+S

(1) Every gas propulsion system shall be so designed and constructed that—
(a) the supply of gas to the engine is automatically stopped by the operation of a valve when the engine is not running at all or is not running on the supply of gas, and
(b) where a reducing valve is relied on to comply with sub-paragraph (a) above, the supply of gas to the engine is automatically stopped by the operation of an additional valve when the engine is switched off.
(2) Where the engine of a vehicle is constructed or adapted to run on one or more fuels as alternatives to gas, the safety and efficiency of the engine and any fuel system shall not be impaired by the presence of any other fuel system.

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Source: https://www.legislation.gov.uk/uksi/1986/1078/schedule/5/paragraph/10 (the official version)
Page: https://openlegislation.uk/road-vehicles-construction-and-use-regulations-1986/schedule-5/paragraph-10
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.