From your post, I cannot tell if the GB material you show is all. What you are showing that is in the stockbook and the covers appear to be in far above average condition. My impressian is the collector went for quality material. What is in the notebook appears to be of lesser quality, but still quite fine. The strip of three 1841 2d blues is very nice. The 1/2d (bantam) plates are very collectable. If that really is a plate 9, you got the you have the one everyone wants.
Collectors often use hingeless mounts in stockbooks if stamps are unmounted. Those George V stamps add up as do the Jubilees. The one crown 1913 Seahorse - if correctly identified - is not a bad one.
I agree with GeoffHa. Not everyone collects postal history and stamps. There are some pre-stamp entires. If you want to sell, you might do better splitrting those. Also, the quality of the GB items is to good to put in a lot of GB & Commonwealth, as the latter excludes specialist GB collectors. A good auction house should advise you on whether or not to split the collection. I would be highly suspicious of one that tells you to sell it as a box lot.
Thanks for mentioning myself and my firm on these posts. All the UK businesses mentioned are honest and would be capable of giving you a good steer on value and method of sale, just ask them to be clear on how long it would take to get back to you. Of the ones listed I'd say pick whoever has offices closest to you.
Is there any indication of where the stamps were bought? Receipts, invoices, etc. There might be a buyer/seller relationship that was already established. That seller might have an understanding of the collection already. It is something I would look for as a potential contact.
I am very new to stamp collecting but as one who sold a coin collection and whose primary focus is coins, the advice offered about what to do with a coin collection is similar to a stamp collection.
a) You will get the price from a reputable and long-established dealer. Don't rush this as I did and sold it to a fairly honest private bullion/coin buyer with the emphasis on bullion. I didn't get entirely ripped off but I would have been better off being patient and selling to a more established storefront dealer.
b) The stamp books will help provide a general organization of the stamps but not too much help with the exact contents unless the book is one with the identification information which you woudl fill in the space. So if you do not have an inventory and original price paid for the stamp the thought of selling this on your own is unrealistic. Even with this info it would be a daunting task. Go with a good dealer/auction house.
c) One thing people forget when they start selling collectibles is the time spent on the project. If you took in account the hourly wage you would be paid to sort and organize a stamp collection you would realize doing on your own would likely reduce any profit quite significantly or have you garner a loss on some stamps. Reading the interest in what you have and the fact it is from very small countries such as Falkland Islands which reduce the stamp from being massively common (e.g. many US definitive stamps) I think you would do well on your own only if you are willing to put in that time. But then again do you have the time? An auction house and dealer will calculate labor in its cost either in what it offers you or the consignment fees if you put items up for auction.
Again YOUR TIME is the most valuable asset you have. Save yourself some and let experts review your collection.