Any question answered...

Up to £6/hr on a meter/pay-and-display/pay-by-phone. Might be a problem if he wants to stay more than 4h as most central ones are time limited. Have a look around on Streetview, there might be free on street parking near Kenton tube, taking a fairly random example of a station which might suit somebody going from Birmingham to Embankment. E.g., there is a controlled zone operating from 11am to noon in Elmwood Avenue to stop people from parking their all day, but if you get there after noon you can just sling it on a single yellow until the next morning.

Thanks!