Have you visited The View from The Shard? A very expensive visit, with exactly the same security checks as Sky Garden. Security in tall buildings is high (even if that security is mostly theatre).

"Certain items cannot be brought into The View from The Shard including large bags and backpacks, over the size of 22 x 15 x 8 inches (55 x 38 x 20 cm) or other large equipment."

"We ask guests to walk through metal detectors, which use a low-frequency electromagnetic field to look for metal items."

https://www.theviewfromtheshard.com/frequently-asked-questio...