DL named driver ncb question

[Z064life]

Hi,

I have (as of next month) 5 years named driver NCB on Direct Line.

I am contemplating whether it is worth buying another car (To build up my NCB). A couple of concerns I have:

1) I can transfer my named driver NCB (Which cannot be recognised by other insurers) to my own policy on DL and which will behave as "normal NCB" (so the same discount).

2) However, the 5 yrs I have will "top up" the full NCB I start to build up in my own policy.

What will be the resultant premium? Will it be from 0 yrs and add up?

I know that there are many questions on this...

Thanks