I think you have misunderstood me. It's true I don't have the knowledge at par with you guys nor I am trying to be an electrician, I am just trying to understand the general bits. If I had no knowledge and I didn't ask here then I would have gone ahead with one of those two electricians, who would have done a shoddy job.Rajshar,
I don't think you understand the knowledge you are portraying. What size is your cut-out fuse? What's the maximum ampage 16mm and 25mm cables can safely carry? If the DNO have attached 16mm to your cut-out why do you want to replace them with 25mm?
Why can't the quoted electricians fit an isolator, that's the simplest job of the lot. A qualified leccy would 100% definitely not allow a customer to purchase the tails and isolator. Too much knowledge is a dangerous thing.
The isolator is being fitted by British gas, the electricity supplier. My electrician will work from isolator. Some of you guys said that they will install 25mm tails and 16mm earth but that will be from isolator. So I asked the question that can I ask the British Gas electrician to fit 25mm tails up to isolator and if required I can provide him the tails. This is the reason I ask the question as I don't know that he will do this or not.
If fuse is 100amp in the cutout then he should fit the rated cables anyway. If fuse isn't 100amp then we will have to ask the DNO to upgrade the fuse and they will only upgrade the fuse if the rated cables are already there. My understanding is that DNO won't touch the tails as it isn't their responsibility.