Hertz LHR are hopeless, hopeless, hopeless.   I will never, EVER rent a car from them again.   The last two times, our booked car was unavailable and they wanted us to take a lesser category compact at the same price I'd booked! (an intermediate SUV).   The most recent time they forced an electric Polestar on me as a substitute for a 5 hour stopover.   When I turned the car on, it said battery life was 50%.  The desk rep said if I didn't fully charge it before return, Hertz would charge me a 50 UK pound recharge fee.  
They are just horrible, rude and unhelpful. I rather rent from Guido's Pizza Delivery and Car Rental than Hertz.  When I put a complaint through UK Resolve they pushed back saying everything was done in accordance with their policies and values.  I was offered 350 points as compensation. Forget it.  Rant complete.