CTC is probably your best source of info on the cyce to work scheme. Here is a link:

http://www.ctc.org.uk/article/cyclin...-bike-and-gear

There is also a forum on the CTC web site with many posts on this subject.

Used Birdy bikes don't come up very often, there is clone made in the far east, have a read of this:

http://www.bikeforums.net/showthread...y-amp-nobirdy?