The consequence of continuing would have been far worse than abandoning. The fact remains that they were moving to put in place democratic reforms. Prior to the Chinese revolution HK was an economic backwater - most of its population being related to the transhipment port and military presence. Kowloon and New Territories were only added as buffer zone for the port. Growth was nearly all post Chinese revolution.
In the post-war decolonisation period GB had a policy of no independence before majority rule. They were putting in place democratic reforms elsewhere, and ensuring minority rule (ie South Africa) didn't continue after independence.
Except that is simply not true, and there's no evidence for it.
British corporations that existed in the HK market may have extracted revenue, as might any corporation, of any nationality with their overseas operations. The Hang Seng is a major stock market in its own right, so the majority of money was staying as HK money. The British government, on the other hand, was not receiving billions into the treasury as a consequence of holding Hong Kong.
In the post-war decolonisation period GB had a policy of no independence before majority rule. They were putting in place democratic reforms elsewhere, and ensuring minority rule (ie South Africa) didn't continue after independence.