Traveling by plane to The Open University
The recommended airports are Luton (40km), Heathrow (90km), Birmingham International (UK, not US!, 99km).
Other airport options apply, but are not as convenient: London City (112km), Stansted (120km), Gatwick (147km).
Traveling to meetings in Oxford by plane
Prof Wild lives in Oxford, some meetings can also be arranged in Oxford:
Heathrow (45 min by car, 60 by bus) and Gatwick (2h by car, 2.5 by bus). Other airport options apply, but are not as convenient: Birmingham International (UK, not US!), Luton, London City, Stansted, in that order.
From Heathrow and Gatwick, you hitch the airline bus to Oxford:
http://airline.oxfordbus.co.uk/ (about £30 for a return ticket).
Traveling by train
Book your https://www.thetrainline.com/ ticket to Milton Keynes Central station.
Traveling by coach
From London: hop on the National Express to Milton Keynes Coachway for meetings at The Open University, or hop on the Oxford Tube for meetings in Oxford.