I personally doubt the government's involvement made any difference to Silicon roundabout whatsoever. It was already well known as our tech hub in those days and the rents were low enough to attract creatives. It was also a matter of time before it became more gentrified and property value 'literally' doubled.
Depends what you mean by tech scene being better, if it's a shortage of tech workers, it's better for tech workers, and it's worse for people looking for tech workers - which eventually affects the decisions about where to base a team. But like another commenter said, remote work changes these calculations.
To make it even more difficult to parse, we also had IR35 reform in the same period!
Edit:clarity
Tech investment in London was growing after the Brexit vote and before the start of the pandemic
The market has stabilized and the salaries demanded seem to exceed what typical "growth and engagement" startup crap is willing to pay, where as before there seemed to be a surplus of talent happy to take these lower wages.
But it's not hard to hire if you have a sustainable business that can afford to pay good wages. When someone complains to me how hard it is to hire I always talk about this magical thing called "money" and where if you put more of it on the table you'll magically get more candidates in the next day. But instead they still focus on pool tables and "culture".
It could also be that the startup market is saturated and the "growth and engagement" bubble is popping? It used to be that any tech company that can show growth (even without a solid business plan to turn that into profit) could get insane amounts of money thrown at them, where as now every idea has been hashed and rehashed multiple times and you need an actual business plan addressing your predecessors' failures - simply boasting how many users you have on your sinking ship won't cut it (or at least not as much).
It isn't even close (tbh, the UK isn't really competing with the EU anymore...the EU is just so far behind).
Btw, the reason why people have moved out of Silicon Roundabout is the same reason banks moved out of Canary Wharf. Rents too high, office space not growing fast enough (Google moved into Holborn, outgrew that, moved to Victoria, outgrew that, and is now building a huge new office in King's Cross). VC funding is up something like 15x since the Roundabout was created, the growth was just too rapid for such a small area.