Wow! I've heard overall Brits consume on the average more than the US, but 4 grams is crazy to suggest is the RDA. I'm sure you'll be fine with around 2300 or so.
I've seen numbers all over the place, so I don't fault FD for posting this, but I'd like to know why they chose THIS value. Yes, one site may say 1.3 grams for over 50 (that's me) but like 95% of health sites will say it's 2.3 or 2.4 grams RDA (USA).
It's darn near impossible to get to 2.3 grams or below unless one is a total vegetarian and cooks EVERYTHING, including condiments. So 1.3 grams is just way too radical to be suggesting to folks IMO.