Thank you for waiting. First, I want to commend you on learning so much about beardie care. Very few dragon owners do that, and then their beardies get sick. You've also been alert to changes and looked for help before a more serious problem developed.
Brumation is extremely unlikely. They seldom brumate before one year of age, and this isn't the right time of year. Brumation usually begins in the fall.
The changes in the viv may be responsible. For a beardie this age, it's best to keep the warm side at least 43.3*C (110*F ). You can do that by lowering the light fixture, but not so low he could be burned by it. You could also return to your more powerful light, but raise it higher above the viv. Temperatures up to 125*F are fine for basking for dragons this young. Your cool side is perfect. For a young beardie, it's better to keep night time temperatures in the mid 70's. 69*F is fine for adults. Your present lighting schedule is ideal. while it seems to make sense to follow the seasons, it's better to leave the lights on for 12 to 14 hours per day year round. We cannot provide natural conditions in captivity, and less light than this can lead to Metabolic Bone Disease, skin problems, and eye problems.
I don't think he meal worms have caused any problems at this point, but even as pupa the chitin content is too high. If you want to feed worms, see if you can get silk worms or Phoenix worms. I'm glad to hear that you feed in a separate place. Uneaten crickets will bite sleeping beardies. The bites, while tiny, often lead to serious infections.
Daily baths were a good idea, but we can make them even better. When a beardie isn't eating well, he can become dehydrated. Adding an electrolyte solution to the bath will help. In the UK, it would be a product called Lectaid, which is sold in pet stores. Soak your beardie for about 20 to 30 minutes twice a day. Reptiles can absorb the electrolytes and fluids through their vents (where droppings pass out), so make the water deep enough to cover the vent. Be sure to supervise closely.
I hate having to tell you this, but I am a bit suspicious that your beardie may actually be sick. While there are some very minor problems in the habitat, they don't seem big enough to lead to any problems. When husbandry is good, appetite loss and decreased energy is often due to an illness or parasites. I would increase the temperature on the warm side and provide twice-daily Lectaid soaks. If you don't see a big improvement within a day or so, I would schedule an appointment with a reptile vet. This link will take you to a directory of UK herp vets:
If you have more questions, let me know in a REPLY. I hope the little changes will be enough to reverse the problems.
My goal is to provide you with excellent service – if you feel you have gotten anything less, please reply back, I am happy to address follow-up questions. Please remember to rate my service only after you have all the information you need. Thank you!