I am not sure if Qantas is still operating non stop to London but that might be a better option , transiting through HK After covid has become problematic and probably best avoided if you can .
otherwise you may have to bite the bullet and buy full fare on emirates to London . Or possibly consider flying through LA or Vancouver and picking up a BA flight from one of those destinations to London . Best of luck to you
you could also request a visa extension due to problems with travel during covid 19 , I believe the authorities are fairly flexible