It's only in 2/3rds of the country though, but it is airing in widescreen, and uncut, so if you've never watched the dvds there's ~15 minutes per episode you won't have seen.
From Digital Spy
BBC spy drama Spooks - known in the US as MI-5 - will air on broadcast TV as a result of a new pact between BBC Worldwide America and nearly two thirds of PBS stations across the country.
The deal, which was negotiated with individual public TV stations including New York's WLIW and KCET in Los Angeles, covers the first three seasons and starts this month. Seasons 1 to 4 were shown in a format edited for screen size and ad breaks on cable channels A&E and BBC America, but were pulled following low ratings. The PBS airings will show the series in widescreen and commercial-free.
"This is a significant deal for Kudos and for MI-5," said Daniel Isaccs, joint managing director of production firm Kudos. "Our belief in its universal appeal has been borne out by the breadth of stations now committed to the first three series. We're particularly proud that it will be seen as it was intended, in its original uncut version. We hope US audiences will enjoy it as much as UK audiences have."