Phil - if you go to FREEREG and search on marriages for Merchant - Shepton Mallet Somerset you will find the marriage for Benjamin Snr, his dad (also same name) + a Charles Hyatt Merchant too.
I wonder if you looked at Burials and Baptisms you might find more rellies as well.
Kanskar
For some reason I hadn't picked this up, but since Benjamin Hyatt MERCHANT (senior) was born about 1809 (according to both 1841 and 1851 Censuses) then the one who married in 1801 must have been a generation earlier again! It looks as if the first Benjamin Hyatt MERCHANT was born about 1780; he was shown as an InnKeeper in 1841 in Shepton Mallet, and as a Harness Maker in 1851 (when he was visiting his son Alfred in Bedminster.)
From freebmd, it looks as if he died in Clifton RD in 1867 (aged 87), so now it looks like there were three generations with the same name:
Benjamin Hyatt MERCHANT (ca 1780-1867)
Benjamin Hyatt MERCHANT (ca 1809-1855)
Benjamin Hyatt MERCHANT (ca 1829-1898).
With this information, I may be able to fill in some of the other gaps such as the marriage of Charles Hyatt MERCHANT in Shepton Mallet in 1819, and of Joseph Hyatt MERCHANT in Clutton RD in 1839.
Sadly,however, this doesn't seem to be the family I started out to research, which was another Benjamin MARCHANT from Shepton Mallet (ca 1802-1862)!
Still, despite the variant spelling of surnames, they are probably related somehow!!
Kind regards and thanks again.
Philip Candy