

Some cafes will do it - not as standard, but a few - maybe try the ones trying to be 1-up from a greasy. https://seahousescafe.co.uk/the-breakfast-menu
As will many hotel breakfasts, there’s often little single serving marmite things in with the single serving jam packets. I’d say about half the hotels i’ve stayed in with decent cooked breakfast have had it on offer.
I’ve also seen it in little roadside food van / trailer type things too.
Anyway, you want sainsbury’s yeast extract instead of marmite, it’s way gloopier and nicer tasting.
Permanent? dont have that busbar flapping arund in the breeze, clip it down. Does that loopy bit have a purpose?
You just need more practice. Reheat some of those, let the iron linger, add more solder maybe flux too. until the solder flows and goes shiny.
The iron needs to dwell long enough to get both parts up to temperature so that the solder flows between both. This means that when heating a larger thermal mass, like the big wires, you need to dwell longer.
You’re heating the parts to be joined, not the solder. Add more flux.
Practice on different sized wires or parts attqached to large ground planes and so on til you get a feel for the thermal mass of the joints.
bigclivedotcom on youtube has some videos on soldering basics. https://www.youtube.com/watch?v=aIab66EgfHM