I'm not sure whether we are allowed to list names but as has already been done in this thread i will do so, Admin if i'm in the wrong delete accordingly.
The above is based on my experiences in the last 6 months, there is a danger some may have changed;
Britannia - Not key carded, discrete access but appearance wise not great. All rooms appear dated as does hotel interior IMO but does the job. Very cheap.
The collection - Not key carded but have to walk in opposite the reception, i've had a girl turn up in discrete attire and still comment on receiving a dirty look from reception staff. Security cameras throughout the halls. Security staff on the halls from 10pm onwards i believe. Decent size rooms but also appears dated.
Novotel - Lifts and stairs key carded. Has a decent size lobby and bar area to meet but as the entrance, stairs and lifts are all in direct eye-sight for reception depending on the time of meet if less busy it can be blatantly obvious who has not arrived together and is heading straight upstairs. Rooms however are nice and spacious.
The copthorne - not key carded and lifts opposite one entrance/reception but i consider it to be fairly discrete. Good size rooms and fairly reasonable price.
Jury's Inn - Not key carded, very discrete due to size to make your way to the lifts unnoticed. Good size rooms and reasonable price.
I can't think of any more of the top of my head but personally i've found Jury's Inn and Copthorne to be the best.
There are a few hotels in the mailbox/brindley place that i'm intrigued to try but am yet to do so, any information on them would be appreciated.
N.B
I should add when i comment on room size and cost it is based a fairly basic room and cost is based on a weeknight booked several days in advance.