My dad lost a lot of blood a couple of years ago. Enough to have us all quite worried. I knew he was getting better when I asked him how much he’d lost and he said “very nearly a legful”.
Listen to the lead up to the punchline. Listen to every word. Of course, ‘very nearly’ is perfect—better than ‘nearly’ or ‘almost’ or… any other word. But every word Hancock says is perfect—chosen to emphasize all the features of the real Hancock’s personality that make the fictional Hancock so grotesque, pitiable, but loveable. For some reason, Pinter won a Nobel prize for literature, but Galton and Simpson didn’t. And now they won’t.
Alan Simpson obit here. (My dad’s fine—he got refilled thanks, presumably, to someone who had ‘a body full of good British blood’  and was ‘raring to go’).
 Just in case anyone misinterprets this, I’m quoting Hancock (who is speaking Galton and Simpson’s words). I don’t for a minute mean to suggest that British blood is any better than any other kind of blood or even, in fact, in the circumstances that my dad got British, rather than some other nationality, of blood, and, just to be clear, he wouldn’t care where the blood came from, just as long as it didn’t come to him over someone equally or more deserving, being a pretty extreme anti-nationalist—indeed I suspect he might prefer non-British blood (as long, again, as no-one else needed as much or more than he did). Mark you, if I ever lose very nearly a legful, there’s not much chance of me being refilled with good British blood since, apparently, however good it is, it can’t be good enough for the American Red Cross. Hancock, of course, is suggesting that British blood is better than other nationalities of blood, and, equally obviously, Galton and Simpson, by getting Hancock to suggest it, are agreeing with me and my dad. Or, perhaps more precisely, they are influencing me and my dad and so many others to have the (correct) view that we have about the relative value of different nationalities of blood.