Rubicund

Is your concern that these time sensitive tests are requested at short notice and you therefore want transport at hand almost immediately? If so and you are staying and attending a clinic in central London, a black cab will be quicker and more convenient. Hiring a car to do this job does not make sense, whatever the reason for it, when you have taxis, tubes and buses near at hand. Parking will be the main problem you will have, unless

Forgive me for stating the obvious, but you are staying as near to your health appointment as possible? The business appointments can be similarly reached.

Your companion will get very fed up of circling the block for who knows how long whilst you're inside.

bilboburgler

Interesting topic, not the offence thing but the whole concept of how to get a car into a congestion charge area.

Surely the clarity is in the concept "congestion".

Have a great day