Calor gas pipe work

[Heathland]

I wasn't sure where to ask this question,I've had a letter from Calor gas saying my gas pipe work isn't up the their requirements,its all plastic pipe work under ground, but as it comes up out of the ground it turns to galvanised pipe,which is lagged with a treated material,professionally done back in 2000.
They are now saying it needs to be plastic all the way out the ground to the regulator,which personally I think is bloody bonkers,putting it politely...
I've got 4 piped regulators,which the pipe work is concreted in the concrete plinth around the outside of the shed plus the down pipe from the tanks,they have said its 3k for them to do the work.
So what is the legal requirements now for this type of pipe work now,or are they just looking for more bullsh*t work.

 

[Bury the Trash]

surely renweing with copper would be ok ? or perhaps you do the work with plastic cant be that difficult ,certainly shouldnt be 3k .