The last stamp on the third row was valued at 110.00 pounds in 2002, so it may have increased in value since then.Like most cat vals...it is extremely over- inflated. That stamp is available on
ebay for around the 8 to 10 UK pounds mark.
Stamps with 4 margins ... full perfs... well centred... nice postmark always adds a little to the value. Take the Stanley Gibbons cat val and divide by eight and that is around the real price for a perfect condition stamp is what I have found.