Impossible Concept#2: Strapping The UK To A Giant Space Whale
Leaving aside the hours of placard-waving that comes with using endangered species as intergalactic propulsion systems, how does this whale even survive in the vacuum of space? There's no food or oxygen for the whale to survive on and any liquids on its tongue are of limited use after boiling away in such a low pressure environment. Its skin is presumably thick enough to stop it exploding due to the immense blood pressure of a creature that size, but if the poor thing gets even one open wound after a nasty meteor collision it's going to end its days looking like a giant fountain pen explosion: bright blue and definitely ruining any nearby exam papers.
Possible Concept #2: Sonic Screwdrivers
Ah, the faithful sonic screwdriver. If there's one thing this machine truly excels at it's destruction, from shattering lift controls like an amateur vandal to the admirably reckless act of opening up a crack in space-time. The phenomenon responsible for all of these explosions and breakages is known as resonance. Every structure has its own resonant frequency and if an external source of vibrations matches this frequency it will cause the object to violently shake and possibly cause some spectacular damage in the process. It's not all mischief and ruin though - the sonic screwdriver also has the potential to protect against sound-based weapons using the same principle behind noise-cancelling headphones: two waves of the same frequency and amplitude will cancel each other out if the second wave is exactly half a vibration out of sync with the first. Contrary to the jokes of several supporting characters, the screwdriver is utterly useless for putting up any shelves. It's a device which encourages someone to go out on near-fatal adventures, not spending the afternoon in their kitchen having strong words with a half-assembled spice rack.