The TIS system available in the US (which is what is being referred to here) is not currently planned for the UK - because NATS have not specified the necessary hardware/software on their radars. Aircraft equipped with (for example), a GARMIN GNS530 and GTX 330 Mode S transponder can quite happily pick up TIS when the enter US airspace.
On another point of detail - There is no requirement for a database to convert between Mode S Hex codes and US N-numbers. The Hex code is a straight encoding of the tail number. Oh the benefits of being "in" on the system early.
2D