This is one of the most asked questions on TruckNetUK and the answer is yes you can.
All you need to do is look at the solo unit and ask yourself a couple of questions.
Q1. Is it a goods vehicle?
A. Yes.
Q2. Is it pulling a trailer?
A. No.
After answering those you just need two more question and you have the answer.
Q1. What licence is required to drive a goods vehicle not pulling a trailer?
A. C Licence
Q2. What licence is required to drive a goods vehicle pulling a trailer?
A. C+E Licence.
No modifications are required to the unit, especially not the ever popular - “You must remove/disable/cover the 5th wheel” nonsense. That was something from many years ago and related to driving a unit on an ordinary car licence. You don’t have to take the tow hitch off a car if you don’t have B+E or the draw-bar coupling from a rigid if you don’t have C+E in order to drive either of those vehicles.