My friend is in a wheelchair and cannot move from there. We need to travel from Waterloo station to the Houses of Parliament - and he needs assistance. He will sit in the chair in the taxi and he also has extensions to make his chair into a scooter. We want to hire a taxi to be waiting for us when our train arrives at Waterloo and then to pick us up later and bring us back to the station - any helpful advise, what company etc would be very helpful. Thank you.