Is the gas smell coming from the gas meter area or boiler area? I

If its the meter area then call your gas carrier, 0800 111999, used to be called Transco, our local one is Southern Gas Networks yours may be called differently, they will come out within 60mins but they will only make the system safe if the gas leak isnt on their property.

If the smell is elsewhere, you'd be better of getting someone local and registered in, if the gas boiler is new, try getting the boiler manufactures to call incase its a fault on the boiler,

Towel Rail should just go back to his supplier and swapped,

Id get someone else to fit the bathroom and tell you pal to do one.