The Complete Power Game DVD Box set, comprising all three series, is currently on sale for £10 extended to 17 September in Network's "Bonkers" sale.
The question was posed today: "Do I need to watch The Plane Makers" before I watch "The Power Game". Interesting question. My answer is "No, it's not imperative." The first episode of "The Power Game" has conversations which refer back to the final episode of "The Plane Makers". They give you enough information to get an idea of what happened in the past. You would probably get extra value from having seen "The Plane Makers" but it doesn't really hurt to have not seen them (When "The Power Game" DVD's were first released, "The Plane Makers" weren't available on DVD).
More importantly, "The Power Game" was written as a standalone series, taking the continuing characters into a totally new situation.
And if you do want to know what happened in "The Plane Makers" we have an episode guide here.