The UK is a weird place, and that is a 1000W vacuum. With all the news going around over there about 1000W vacuums being "illegal" - I am sure someone might have been scared of getting arrested and tossed it out based on what tabloids said.
Also, for mold and fleas, both of those can be cleaned up with soap and water, and with special flea killing aerosol for fleas. Mold does not continue to grow once it leaves its host environment and it will go dormant until growing conditions re-appear. Mold can be washed with soap and water and it's good to go. There is no hazard with mold unless you have allergies to it.
Fleas will not survive if the vacuum has been outdoors for more than a day or two because there is nothing for them to survive on and they will seek better protection if they do not die completely within the vacuum.
I really do not mind about dirty vacuums, that is what their whole purpose is, and not everyone treats them as a million dollar collectible. I have vacuums that I have not cleaned up yet awaiting a full refurb, and all of them are packed to the brim with dirt and debris, and no hazards have resulted from having them in my home temporarily with their full bags. If there ever came a day when someone didn't ship me a dirty vacuum they should be President!
I do wear a mask and goggles when using an air compressor with a blow nozzle on it on the pleated HEPA filters since you can get kickback on the dust sometimes or if the wind blows the dust cloud back at you, but that's about it. Spreading the pleats apart gently and blowing out deep in the cracks does salvage the life of the filter a little for long enough until you can replace it, but I always replace it anyway because who knows if it's ever been changed at all since the vacuum was off the assembly line.
I would dismantle the vacuum completely, wash all the plastic bits that are not sensitive to being wet and dust off or oil the motor if it sounds rough and then reassemble it. Gives you a chance to inspect for any broken or missing partzs too. Henry's are pretty common and they didn't change much so it shouldn't be very expensive to replace the attachments and hose if you want to keep it. Good luck!