Welcome!
You say you 'put the film in for scanning'; I suppose the same people did the developing too? If you're getting consistently disappointing results from one lab, you might just try another one (I suppose it's also possible they can develop film well, but their scanning is no good; if its bad scanning, you might still be able to get better scans of your negatives).
We will need to see an example or two (more, preferably) to comment. Details of your camera would be helpful too.
Before seeing those though, I see you're in London, and your photos were in Sydney. Did you get the films developed in Sydney, or transport them back undeveloped? Airport security x-ray can be bad for film, though the effect (at least the effects I've had) isn't to increase the grain.
Saying you pushed film is a red flag to some people here, but I have always done it, to keep shooting as the light fades, or on cloudy days in winter. You need to be reasonable; some film pushes well and some doesn't. Even with film that the maker's say pushes well, you shouldn't expect to go more than a couple of stops, and you will be able to see it was done. And of course, you need to
tell the lab you pushed, and what speed you used, so they can adjust the developing.
Are the photos from the first half of the pub crawl any better than the second half? Working on a backup theory here...

