It’s not a particularly new problem. Over fifteen years ago I was flying at 1300 feet in the LHR CTR (then class A) when an aerobatic R/C model aircraft flew vertically up in front of me, just outside the rotor disc. I’d estimate it had a 1.5 metre wingspan and it passed close enough to see that it had a tuned exhaust pipe along the side of the fuselage. It was being flown just north of Brent reservoir. I reported it to ATC but nothing came of it.