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Direct answer to my questions as they weren't answered on point (not all of them):
Will we be able to board a later bus if the landing in Luton is delayed [and made the coach reservation online with a fixed boarding time]?
Answered by Uciebila. (tldr: probably yes) We didn't buy tickets online, we brought them at the airport, on the spot.
Will we be able to board an earlier bus (for the return trip) if we feel traffic is going to be a problem [and made the reservation online with a fixed boarding time]?
We did exactly this, but we purchased the return ticket from the airport when we arrived (it didn't specify the exact boarding time for the coach).
Will they be more expensive [if we buy the coach tickets on the spot]?
No. Same price as online.
Where can I purchase them "on the spot" for the return trip, the driver, ticket machines in Golders Green/Finchley Road station)?
There are ticket machines and an office right before the exit doors from the Luton airport. We used the ticket office and I asked for return tickets, which did not specify an exact time for us to board the coach, hence we were able to use any bus (both for Luton-London and London-Luton). Sure enough the first return bus that arrived at the Finchley Road station was fully booked and the driver couldn't allows us to board, but the next bus arrived after 5 minutes and was pretty much empty, so we boarded that one.
Is there a Green Line bus every 30 minutes?
The National Express coaches were sufficient for us, so I cannot say.
Upvote:4
The trick is to book through easyBus. First, their FAQ notes
Donβt worry, if your plane arrives early or late, you may use the same ticket at no extra cost to travel on the next available bus, up to 60 minutes either side of your booked time. Please note we cannot always guarantee there will be spare seats, especially at busy times since passengers travelling on their booked service have their seats reserved and will be boarded first.
Second, observe their route map -- most of their London routes are not operated by themselves but "by external coach service", in this case, National Express.
Upvote:14
They have no obligation to take you on a later bus, but I have seen sympathetic drivers allow people to do it in the past. I very much doubt you would be able to get an earlier one.
You can book tickets on the spot from your phone or a ticket desk, they might go up in price or sell out though. If you choose the 'amendable' option it allows you to change your ticket for a different one at any time before the departure of the bus (and as many times as you want) so this would work for taking an earlier or later bus as long as you did it before your original bus left. (source)
Another alternative is to purchase a Β£5 add on (presented at check out) that allows you to do the following:
For just Β£5 each way, our Change & Go Add On lets you be completely flexible with which coach you board to and from the airport:
- Board any available coach 12 hours before or after your original departure time
- Amend your ticket to a new departure date - free of charge
- Refund on your ticket up to 24 hours before departure
(Source)