Now an investigation by the Health and Safety Executive is under way, and a spokeswoman for the organisation said it was still collecting technical evidence.

Gas safety experts said use of plastic put residents in "immediate danger." But the firm behind the two-year-old Iceworks on Cross York Street, Leeds insists the piping met regulations.

Darren Smith, commercial director of Urban Edge Group Limited, which built the flats, said the gas fitting was carried out by a registered Corgi installer and "designed and specified by our professional consultant."

He said the units were "completed and signed off by Leeds Building Control and Premier Guarantee Insurance as constructed in accordance with the design and current regulations at the time of the construction in March 2006."

Mr Smith told the YEP: "We have investigated with our consultant and subcontractor to determine why the gas pipes were installed in 32mm MDPE (medium density polyethylene)]. It is our understanding of the regulations that gas installations deemed as "external" can be installed using this material, and the installation at the Iceworks was considered to be external."

He said the firm's priority was to restore the gas supply to residents.

It has been working with Yorkshire Housing, which owns the block of flats, and the gas authorities to find a solution.

A spokeswoman for Yorkshire Housing said it asked Corgi – which oversees the safety of gas installations – to visit Iceworks after its own inspection raised technical concerns. Northern Gas Networks, which owns the local gas distribution network, was called in and cut off the supply.

Ged Walsh, director of development for Yorkshire Housing, said the contractor had agreed to replace all the gas pipes. Pipe replacement work is expected to take around three weeks, although a start date has not been given.

He said most, if not all, of the 25 flats had now been fitted with electric water heaters.

Tenants will receive a rebate, to be calculated when the work is complete.