Most of the large train companies in the UK have a contactless smartcard system, where a ticket can be loaded in to a card after-which all the user has to do is tap in and out at the departure and arrival stations.
As this is not entirely clear to me at the moment, after asking at my local ticket office, do all contactless smartcards allow for use on all networks?
For example, could I use a Thameslink smartcard (branded as "The Key") on an Avanti West coast service?
Yes, depending on where you buy the ticket.
For your example, Avanti website says
you can buy any available smartcard ticket. It doesn’t matter if the ticket is bought through another train company or whether it is for travel on another train company.
Avanti allows online purchase of Season tickets, Anytime, Off Peak, and Flexi Seasons tickets, while Thameslink only lets you have Anytime or Off-Peak single and return tickets bought at ticket offices and ticket machines on its Key card.
