OK, firstly, "beardeddragon.org" is a dead site, it has been for years, and the information on it is everything from out of date to actually harmful....
RSPCA, well intentioned as it may be, are not particularly knowledgeable about reptiles in general... dogs, cats, hedgehogs...sure... reptiles not so much...
You also need to look at when that information was last updated, in the past decade reptile care has made some huge leaps forward.
Secondly, read through the link about substrate choice and impaction, impaction is something that has been greatly misunderstood for years, and in the last 5 years or so people have started to understand the actual genuine cause behind it when it comes to loose substrate. Its not the substrate, its the environment and provision given to the animal that then leaves the animal in a position that it cant properly deal with loose substrates, which it normally would (Cold blooded animals have evolved in a way that they are literally keyed into a specific environment/habitat... if thats not spot on, then they dont work properly.... easiest way to explain it)
If you are providing proper temperatures, lighting, hydration and diet (as you should be for the best care of the animal) then loose substrates (assuming you choose one thats a decent representation of their natural "substrate" in the wild) arent going to cause problems.
Leos should be setup so it mimics their wild habitat, you should have flat (real) stone in there positioned under a basking lamp that runs during daylight hours. You do not need night time heating unless the temp in your house drops below 16C at night, which is uncommon in a house with central heating.
The stones will sit and absorb heat/energy and then slowly release.
Leos are crepuscular, so most active as the sun starts to set and rise, meaning they dont get full exposure to sunlight but they DO get exposure, you have to consider that in the way you light the viv its in.
They are also evolved to be highly effective at absorbing UV light, because they have a limited timeframe in which they are exposed to it, but its still a key part of their biology.
So, with that in mind;
Basking lamp setup in a viv that is minimum size of 3ft long, 1.5 ft deep/high (preferably 2ft to give better height and greater floor space)
Basking lamp at one end, with a small UV light over the basking area.
Lights set to be on during the day only, and temperature controlled so the basking area (which should have lots of natural stone in to sit on and bask on) is roughly 35C during the day (SURFACE temperature, not ambient...important distinction...the two temps will NOT be the same as each other)... this will start to drop off once the lamp goes off, the rocks retain the heat, and viola - one natural basking setup created to mimic the same way that a Leo has naturally evolved to bask and get low level UV exposure.
Multiple hides in, and heavily shaded areas in the viv, the warm hide should be setup near the basking area so it to is warmed and retains some of that warmth as you go into night hours. Sand/Soil based substrate, pressed down so it creates a firm surface but can also be dug into (there are prepackaged ones, you can make your own... lots of choice here, I personally favour a clay based soil mix with fine sand, compressed down so it will dry on top and give a solid layer, bits in the shade will be softer and it can dig into them and it will also then help maintain slightly better humidity where the substrate layer retains some moisture)
You may well think its enjoying the heat mat at night, and it probably is, but that cycle of warmth and then cold at night is part of its biological cycle, its evolved to function with that set of parameters.
It will like the warmth because its cold-blooded, so its instinct tell it to seek out heat sources. Doesnt mean it should be doing that at 3am in the morning when the rest of its biology (like some of the enzymes involved in digestion for example...) then require a temperature dip to properly function.
I'll leave it at that, what you choose to do is up to you, but the point I am making is this.
Husbandry and care moves on, knowledge about these animals has greatly improved and understanding more about these animals biology has also meant we are in a better position to provide an environment in which that animal doesnt just survive, but can actually thrive as it works with the animal, rather than just meeting the minimum requirements to keep it alive.
