In response to my previous post, Dennis asks about which catalog to use for more details about Machins. It's an important subject but not one that has a simple answer. I'll post a few of my thoughts here.
Charlie posted a note about Douglas Myall's The Complete Deegam Machin Handbook. I think it's the most popular with readers of this blog as well as on the Machin Forum. It's my favorite, too. While the print edition is very costly (I think now one has to buy the basic handbook and a supplement), the CD-ROM version is, I think, £40 post paid. (Don't quote me, get the latest ordering information from Myall at firstname.lastname@example.org.) Also, you get free updates by email, and you can trade your CD for an updated version at any time for half price. (Don't lose your original; you must return it to Myall.)
Granted, the CD isn't as convenient as a physical book in some respects (though it is more convenient in others, I think). However, the price may make it all worthwhile.
Another alternative is the Machin Collectors Club's Queen Elizabeth II Specialised Definifives Stamp Catalogue. It is available from the club for £36 plus £10 postage to the U.S. I personally don't recommend it because of its very awkward organization scheme, but there are many collectors that do use it. Unfortunately, I can't think of a way to get a look at it before buying. I intend to review the catalog on my web site one of these days, but that day won't come for several months, I suspect.
There's also, as Charlie notes, the Stanley Gibbons Great Britain Specialised volumes. You have to buy two, one for pre-decimal issues and one for decimal issues. The latter hasn't been updated since 2000, making it not very useful. Hopefully a new edition is coming soon.
Another possibility is to use one of the intermediate catalogs. They aren't as detailed as the ones I mentioned above, but they do go beyond the basic listing in the Scott catalog. The two intermediate ones are The Stoneham (produced by the Machin Collectors Club) and Gibbons' Concise.
I reviewed them on my web site, though I didn't concentrate on their use by Machin collectors. Of the two, I would recommend the Concise for Machins, again because I don't care for the Stoneham's organization method.
The bottom line - if you are serious about Machins, scrimp, save, cut corners, do whatever you have to, and get the Deegam.