agree, very good find. For whatever reason, Registration 418885 is missing from the list in Jenny Thompson's book - in theory it would occur somewhere around early October 1903. The reason for absence of the No. in the usual glass lists might be that the Board of Trade have entered this one in CLASS I, which was intended solely for items of metal, rather than the correct CLASS III for glass.
I can look for this one next time I'm at Kew, unless of course you're able to locate details in the meantime. It's unusual for a Registration No. to be wheel engraved, but there are precedents - on some Stuart glass from memory, on non-pressed items.
P.S. Looking closely at the base of your shaker, I think your No. in fact reads 718885 - the first figure isn't a four - is that a possibility Petra? This would make more sense, since the era for cocktail shakers was the 'roaring twenties' rather than the first few years of the C20, and the Blue Book gives a date of 08.02.1926 for Registration 718885. This design Registration was allocated to O.S. Middleton, whoever they were - perhaps you might dig around for some information on that name.