I usually go have my cleaning session at Smilepod Covent Garden as they are always very friendly and the therapist is very nice and professional.
They always take me on time and take the time to explain everything and review my teeth / gums from the last visit.
I had booked a cleaning session and coincidentally had a toothache the weekend before. Smilepod was good about changing my session to another branch where I could also have an emergency check up, including x ray. The latter service wasn't cheap but I figured out the problem and my toothache is gone.