Do you know why it's recommended to not give dry meal worms? I don't over-trust information that comes without a why. It just seems incomplete. I don't see why meal worms would be any different in the UK than the US or Australia.
If all they eat is Layer, it should be enough of everything they need to stay healthy and lay eggs, a balanced diet. But if you give them other things, then all they eat is not Layer. It's generally recommended that "treats" form at most 10% of their daily diet. That doesn't help much does it? If they can't clean a treat up in about 15 minutes, it's too much.
One good high protein treat is BOSS (Black Oil Sunflower Seeds). Those give a nice protein boost. But you do not want to overfeed them, just a few is enough. The Black OIL Sunflower Seeds are pretty high in oil, you don't want to overdo that but it will make the feathers nice and shiny.
Some people feed cat food. Dog food is often too salty.
Many people won't like this, but another high protein treat is meat. Mine get cooked meat from table scraps but I also feed raw meat. If I trap a mouse they eat the mouse. When I shoot or trap a predator or pest, they might get to peck at the carcass for a while before I dispose of it.
If you thought that was disgusting, just wait. Or don't read any further. Some people feed them maggots. They make it sound nice by calling them black soldier fly larva. They put meat up on a platform protected so that the chickens can't get to it. The meat rots and stinks to high heaven. That draws flies that lay eggs that hatch into larva (maggots). The platform has slots for the larva to fall through to the ground, where the chickens eat them.
Now, what did they say was wrong with meal worms?