http://www.bbc.co.uk/news/business-33063748Apple Pay works with Apple devices with the appropriate NFC Chip - that means iPhone 6 models, and the Apple Watch (which will bring Apple Pay to iPhone 5 S owners). A lot of UK retailers are going to be onboard, including TFL - taking payments on busses and the underground.
That means to travel on the Tube, you can place your Apple Watch near the scanner, and you’ll be let through the barrier. OK - there’s a flaw there. Most people wear their watches on their left wrist. On the barriers to Tube stations, the sensor is on the right as you walk through. So using your Apple Watch to pay for your journey may be a bit awkward.