Thanks all. I used Speranza's suggestion as a guide, worked out the tin size, converted it to sugar and converted that to Splenda. It was about right sweetness-wise, but nowhere near as nice as Heinz or Branston.
By the way, I hardly ever do the convenience food thing, as we just can't get the brands here, or if we can, it's ridiculously expensive (2€ or about £1.50

) for a tin of heinz baked beans But my OH who is French does love baked beans with his SW full English breakfast. With HP sauce