When you apply for a remortgage, just like a mortgage, the lender will require you to have a valuation done.
A simple valuation (as opposed to a Homebuyer report, which is common when buying a property) is typically sufficient, as the bank only cares about the value of the property; the additional content of more detailed surveys are for your benefit, not the bank's.
Although simple valuations are sometimes referred to as being "drive by", that's not very accurate! A surveyor will visit the property and have a look around.
You're not likely to have any input on the valuation. However, the mortgage application happens before the survey is instructed, so you have to estimate the value of the property at that time. One could speculate that that estimate may influence the surveyor.