To be clear this is all spitballing, counterfactuals etc.

MI6 suffered a string of defections to the USSR in the 50s and 60s, which hurt the organization and put it in a "defensive crouch." Since intelligence production was very important to the US/UK relationship, this put MI6 in a position where it would be relatively eager to accept the bonafides of a new UK-based KGB "double agent" that dropped into their lap. And so dropping one into their lap in the 1970s would make plenty of sense.

But this does not mean anyone had a real plan on how to use Gordievsky at the time. And in fact, he's immediately recalled back to Moscow on some pretext.

In the 1980s, Andropov begins running around looking for a pretext to launch a nuclear war. He can't do this as KGB chief, but he's doing everything he can to assemble the evidence for it. And the writing is on the wall by 1981: soon Andropov will become to General Secretary, where he will have the authority to launch missiles. Somebody needs to defuse this situation, but you can't tell Andropov he's insane and there's no official channel to warn the West.

Coincidentally, and about four months before Andropov becomes General Secretary, Gordievsky re-appears. But now he's been turned into an irresistible dream asset, maybe the best human intelligence asset the UK could ask for: a high-ranking intelligence officer at the KGB station in London, clearly on his way to running the place. He should be able to produce all kinds of information that would immediately shut down all kinds of operation.

Except curiously, Gordievsky produces almost no really valuable information that would hurt the USSR. The intelligence he carries with him is described as a "trove", but on closer inspection, this stuff is juicy but utterly worthless: just a bunch of aging lefty political figures who aren't producing useful intelligence for the KGB and probably never did. But surely Gordievsky will expose dozens of London-based KGB spy networks? Except weirdly he doesn't do that, either; conveniently the main "intelligence" finding he delivers is that there are no KGB spy networks in London, so there is nobody to burn.

In fact, almost the only real piece of intelligence Gordievsky ever offers is the fact that Andropov is panicking and trying to assemble the case for a pre-emptive strike. He delivers this information instantly, and then delivers it again and again. When Able Archer happens, he rings the alarm even louder. This doesn't compromise the KGB one bit: in fact the result is entirely advantageous to the USSR, since it convinces Western militaries to back off.

He then gets promoted to an even more important position, where he basically becomes a political go-between transmitting information from the Russian leadership to the West. At one point he's basically writing Gorbachev's speeches, while convincing the West that Gorbachev is legitimate. The result is also not harmful to the USSR: indeed, it ensures that Gorbachev's visit is a resounding success.

My point here is that if the USSR wanted to deliver a high-level agent that could provide "useful" information (from the perspective of the USSR) while doing minimal damage to the USSR itself, they would have had a hard time doing better than Gordievsky. And it makes plenty of sense to exploit the UK's desire to be the conduit for such information, rather than sending Gordievsky to Washington where he would be one source among many.