That's the worst part, with eligibility we can say 1-2 months, but with background checks no one knows. I have seen people on forum that have pre-arrival since July but their background checks are still in progress.
I'm not sure why is it like that. People who have cases allocated to Mississauga office or example, are done in 3 months, including background checks. Then why not for London? Well no one knows. Whether it's a different process for Pakistani applicants due to our political history, or whether it's visa officers that do not finalize in order, or go back to applications to update them time to time, we don't know.
All we can say is that keep your fingers crossed and pray that all of us, and specially you, are freed from this misery.
Have you passed your eligibility/got the pre-arrival?
Thanks.