In message , Paul Corfield
writes
There were huge issues in Hong Kong with Octopus when the
cards gained significant take up and then Creative Star (the operator of
the system) started to hold vast reserves of electronic cash and also
started to tie in other retailers. The Banks in HK got very nervous
indeed and IIRC special steps had to be taken to regulate Creative Star
within the banking sector. There *may* be similar issues here but I
don't know for certain.

There are very onerous e-cash banking rules in the UK, as well. I'm not
an expert, but I think they only kick in if the cash can be spent with
third parties - and is therefore in some sense part of a public
transaction. How any of this applies to Oyster, I don't know!
--
Roland Perry