James Penton wrote:

What's also strange is the amount it deducted - GBP1.10. The Tramlink
PrePay should be GBP0.80 single. The only guess I can make is that
this
is the single or two-zone Tube PrePay fare, but I touched out at
Wellesley Road which you can't get to with Tube PrePay, and it's 3
zones
between Wimbledon and there. All very strange!

I think you must be right about the barriers at Wimbledon not knowing
whether you're going on the Tube or Tramlink. However, you're not
supposed to touch in and out on Tramlink - you touch in when boarding
(like when boarding a bus) and it deducts 80p. Presumably if you touch
on the reader when you get off the tram, you will get charged another
80p (and so on until you reach the appropriate cap).

So, in short, it sounds like you have to touch in twice at Wimbledon
(which is very counter-intuitive) but not at all when you get off the
tram!