Quick mortgage porting question

Hi, just a quick question if I may, as I can't seem to get my head around it:

I'm half way through my mortgage of £125k, having paid off £50k roughly.

If I want to buy a bigger place, can I port the mortgage across, and use the £50k that I have paid off as a deposit?
(Port the remaining £75k on the existing rate, and get another mortgage for the extra £100k or so that I want to borrow?)

Thanks in advance

Andrew