Apple Pay rolled out in the United Kingdom this morning, with support from American Express, MasterCard and Visa, as well as MBNA, Nationwide, NatWest, Royal Bank of Scotland, Santander, and Ulster Bank.

Bank of Scotland, HSBC and its subsidiary first direct, Halifax, Lloyds Bank, M&S Bank, and TSB are prepping their systems and will be available soon. Obviously, this list will expand as Apple signs up new Apple Pay partners.

One prominent use case, shown in this image, is the use of Apple Pay to pay for the tube or metro. Think long lines, combined with short transactions. Another similar case would be entry to a stadium for a concert or sporting event.

The Apple Watch is perfect for these sorts of transactions. No reaching in your pocket or backpack for your phone, something made even harder in the crush of a long line in a crowded metro or tube station. In these settings, the value of Apple Pay is leveraged by an Apple Watch. As useful as the Apple Watch is in a meeting, the additive efficiency of a long queue of similar transactions, each made slightly faster, makes a strong case for the long term prospects of the Apple Watch.

As Apple proves time and time again, it’s all about the ecosystem. Apple Watch, Apple Pay, Apple Music, iPhone, iPad, and the Mac all contribute to the ecosystem. In return, the ecosystem adds value to every device Apple rolls out to the consumer.