What is the most common term for grandmother and grandfather in the UK?

For the male grandparent we would normally use grandad. It can also be spelled granddad, but grandad is more usual. Grandpa is also quite common, but it suggests an older man (not many 45 year olds would like being grandpa!). You can also come across pop or pops, or gramps.

For female there are loads of terms of endearment. Grandma, granny, nanny or nan. Grandma and granny again imply an older lady --- young and glamorous grannies prefer nan often.

We sincerely have quite a few phrases for Grandfather and Grandmother they are; Grandfather: Grandpa, Grandfather, Grandpop and essentially the most fashioned one used is Grandad. Grandmother: Grandma, Granny, Nanny, Nannie and probably the most customary one is Nan. It relies, every body i do know, and all of the playing cards in the card shops say Grandad. However Grandma and Nanny are equally used for a Grandmother relying on what the character likes to be referred to as. I'd use Grandma though so no one get's careworn with a babysitter. (Which can also be reffered to as a Nanny).

Nan & grandad.

Some others are

nanny. grandma, granny and grandpa, grandpops.