Georgesgran
It’s not the end of the World to take short cuts. I believe Bisto Best granules are made with meat juices. Some recommend adding meat juices to the granule gravy, and make it with the vegetable water. I always use granules, for vegetarian gravy for myself.
I use the Bisto Best Gravy granules if I'm rushing, the lamb is particularly nice but a bit salty so I often add veg water and meat juice, and thicken it if necessary with plain flour or potato flour.
Personally I don't much like the texture of cornflour gravy, but a lot of people do I know.
If I'm cooking something that gives out a lot of liquid, like turkey, I boil it down to reduce it whilst the meat is resting and then thicken it with one of the flours mentioned. Of course there are giblets too so I make the stock from these the day before and add this too, though I don't put the liver in.
I use gravy browning too, though I had trouble finding it last time I ran out.