Hello and welcome to the forum. I'm just south of Peterborough so guess not too far from you.
I wonder what's the age of your SIB? Glue does have a life and often once you find a leak there will be more to come. But lets hope your leak is just a one-off weak join.
It's a difficult location to glue. The by the book way would be to heat that whole circular seam and prise it apart with a plastic scraper then clean with MEK and re-glue with a proper inflatable boat two-part glue. Taking note to follow the very specific instructions re temperature an moisture levels.
However were it mine as Oldman2 says I'd use Stormsure/Stormseal...
Inject it in so it is right through the width of the seam.
I have used this to repair my HP air floor and it's been fine for years despite my initial reservations.