Sometimes a visa office will elect to extend the medical results in order to give an applicant time to land - but that is completely at their discretion. Seems you're really close to the outside limits of London's processing times - have you
ordered your CAIPS notes for information about what has delayed processing? London is actually one of the "smoother" offices as far as processing is concerned . . . but it's typical of any office to put a "complicated" application on a shelf somewhere. Buffalo did the same with ours . . . complication, so they stuck it in a pile somewhere and nobody touched it from June 14th until December 19th. I know you're in London, but if you have family in Canada, you could try to contact their MP and see whether they'd be willing to make an inquiry on your behalf. (I wouldn't tell them you're
living overseas.)