Kitchen mixer tap. 12 yrs old. needs new cold tap as the bit you turn no longer grips. are they standard size?

Local diy store says i need a whole new unit at £50. its the handle that spins on the spindle that has worn away so it doesnt turn off properly. can anyone advise me if i can get a standard size fitting for this or is the local store looking to get me to buy their new tap?
Answer
The shaft inside the tap could be different lengths,take the old one with you get a new one