Here is an old English pattern teaspoon (13.5cm, 15.5g) with a single drop and an unusually long bowl. It was hallmarked in 1795 London. I'm not sure of the maker; could it be John Baker II?
John Baker ll had a pellet between the mark, John Bourne entered a mark as a spoonmaker 2/2/1774 he also entered a mark with a pellet 7/5/1774 but for smallwork 22/7/1774 he left the pellet out and on the 24/1/1778 entered a slightly smaller mark (without pellet)
I tried leaving a post on this over the weekend, but had trouble doing so, and now I am away from home. There is another maker whose name is now escaping me, who is listed in Grimwade's as having an earlier initial mark than yours, but who Grimwade also identifies has having a later mark that is bolder that was used in 1792 and later. This would match with your spoon's dates. If anyone has Grimwade's handy, maybe this will be enough of a clue to look it up. Otherwise, I'll be home tomorrow evening and will look it up and repost.
I am back at home with my Grimwade's! The mark looks similar to the originally registered mark of John Blake, although the mark shown is not as "fat". However, according to Grimwade, he used a "similar, slightly bolder" mark in 1792 and 1795, which fits nicely with the date marks for your spoon.
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Bourne's mark is similar, but not quite as broad as your mark. In addition, Bourne's marks were all registered in the 1770's; I haven't seen anything for John Bourne in the 1790's but it is possible.
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The picture in my second post of this thread is a John Bourne mark from 1793.
The John Blake mark I posted, although admittedly made later, has much more prominent serifs on the I than my mark does. Was a change made in his mark between 1795 and 1810, or has the I on my mark been mistruck?