wrote:
http://www.theregister.co.uk/2012/02..._for_tfl_data/

"The Metropolitan police has requested Oyster card data relating to
citizens
and other personal information from Transport for London (TfL) more
than 22,000
times since 2008"

And if anyone brings up the old cliche about "if you've nothing to
hide.."
etc, can I assume you don't have curtains or blinds in your windows at
home?


It doesn't say how many of those requests were granted, as it's not
automatic - though if the police have their wits about them they should
have worked out by now how to avoid submitting requests that don't hold
out much chance of success.

Perhaps worth noting this para:
---quote---
TfL said that it could not provide a breakdown of the number of requests
made by the Metropolitan police just for passengers' Oyster card data
alone, but a spokesman for London's police force told Guardian
Government Computing that the majority of requests were likely to be
related to Oyster information. Other than Oyster data, personal
information requested would include CCTV images and details of TfL
staff, he said.
---/quote---

Also, just because an Oyster card isn't registered doesn't mean that
data relating to it cannot be requested.