Ten W.
I used to be cabin crew in the 80's and also used to operate the routes you mentioned on 1-11's and series 2 737's.
On the Jersey route if all tourist on a 1-11; 99 pax, we used to have only 2 cabin crew at one time and 3 on the 737. The service was not exactly as you stated a full meal. It was just a combined drinks/ bevs/ biscuit service exactly what they offer in tourist now The main difference is we only did that on only the very short routes not on the longer routes as they do now.
We did it then and as you say the 737 was about the same capacity as the 319, we managed it then without refusing pax drinks and as far as I remember there were never any health and safety issues. It was a rush especially on the Jersey route but we managed our service effeciently to suit the flight time. It was possible then so why not in now?
LGW crew operate the LGW-JER on a 737, perhaps they can explain how they do it.
I would like to add that on flights just over about an hour we then did a cold meal, drinks Bevs and a proper duty free service, I cannot remember how many crew we had on a 737 on but it was probably only one more than they will get from tomorrow for just a bar service+ cookie and the tax-free service which did not compare with the time it took to sell proper duty free itmes. There also was a time we charged for drinks in tourist added to the above, that was time consuming.