Legion, if you want to run gas through a drinking straw, that is not a problem. It is not a problem until an incidence takes place. Building control or Health and Safety might or might not be aware of shortfalls on a building site. If there is an incidence, no doubt about it, the last person resposible will certainly loose his head.
Following section is cut and pasted from Gas Safety (Installation and Use) Regulations. I hope it tickles your funny bone.
Enclosed pipes
19.—(1) A person shall not install any part of any installation pipework in a wall or a floor or standing of solid construction unless it is so constructed and installed as to be protected against failure caused by the movement of the wall, the floor or the standing as the case may be.
(2) A person shall not install any installation pipework so as to pass through a wall or a floor or standing of solid construction from one side to the other unless any part of the pipe within such wall, floor or standing as the case may be—
(a) takes the shortest practicable route; and
(b) is enclosed in a gastight sleeve and the pipe and the sleeve are so constructed and installed as to prevent, as far as is reasonably practicable having regard to paragraph (1), gas passing along any space between the pipe and the sleeve or between the sleeve and such a wall, floor or standing as the case may be.
(3) A person shall not install any part of any installation pipework in the cavity of a cavity wall unless the pipe is to pass through the wall from one side to the other.
(4) A person shall not install any installation pipework or any service pipework under the foundations of a building or in the ground under the base of a wall or footings unless adequate steps are taken to prevent damage to the installation pipework or service pipework in the event of the movement of those structures or the ground.
(5) Where any installation pipework is not itself contained in a ventilated duct, a person shall not install such installation pipework in any shaft, duct or void which is not adequately ventilated.