UK Landlord Forum / Life

Hi, im hoping someone can shed some light on this ..

I moved into a property 4 years ago, it was a new build built by the landlord himself. I registered all the utilites, even had a tv point/phone point put in as these had not been installed during the build. After a few years it turned out that i was only paying for electric, not gas and electric as i'd thought ( i thought my husband was dealing with the utilities/he thought i was and a direct debit was set up so caused no real issues) any way when i discovered this i called all the providers to find who was responsible for the gas and failed to find out who was in charge of the source. I even called a central hotline that can apparently do a search but could not find out who was resibile for it, or who i should pay.
We shortly after moved out of the property and the landlord is refusing to give us our deposit back until the bill is settled. I can completely understand why he is doing this but i have explained that outstanding bill is our liability, the energy companies lodge the debt on us as a person- not a property. He now has new tenants in and they have since registered the gas.
What im asking is was it the landlords responsibility to register the Gas when he built the property ? it seems a gas meter was fitted but never registered - anthoer thing he kindly left for us to do.