Rented a car on the 4th for a few days. I always rent from Europcar in Heathrow who are also fantastic, but this experience too was smooth sailing. The lady who processed the booking for us at the counter (can't remember her name, really sorry!) was super friendly. She offered us an upgrade for our wedding which was an unexpected surprise and wished us the best. Her colleague who seemed free when we walked in didn't even have a greeting to offer us though...so we were a still a bit wary. But there were no issues returning the vehicle and the prices were very reasonable.
I'd always suggest THOROUGHLY checking the car when you pick it up and take photos when you return it. These companies if they see something that hadn't been reported by the previous driver or because they missed it last time will seek to get reimbursed for the damages and naturally you'll be liable for it.
p.s. The car park is fine for regular cars but I imagine navigating a van through the entrance might be tricky. Would recommend checking other branches.