Some unis seem to deal with all the international and contextual offers first. Durham seem to do this and LSE. But it really varies by department. For instance, at Durham, the large 'flagship' courses take ages - History, English, Geography.
DD applied in Year 13 with predicted grades A star, A star, A (plus A star EPQ). Offer from Bath within a week (I think it was ABB - lower offer due to EPQ). Offer from UCL was in Nov (I think it was A star A A). Had Oxbridge interview, but rejected in Jan. Offer from Durham in about March (A star, A, A). LSE never replied! Their deadline came and went in May. They do not answer the phone in admissions and do not reply to emails. So she just gave up by May and firmed UCL. Who knows if they would have offered in the end, but you get past caring. They had held her application since the previous September.
Then she suddenly decided to reapply and take a gap year, so declined all offers (yikes). This time she had three A stars, plus A star EPQ achieved and some national essay competition prizes, super curricular things and plans for gap year that were very relevant to the degree. Received an offer from Bristol within a week. Got into Oxbridge in Jan, but had still not heard from UCL, Durham or LSE (god knows why she even applied there again) by this point. But she just formed the Oxbridge offer and didn't need an insurance second time round. So who knows if the others would have offered or not. LSE is notorious for keeping people hanging until April / May. No idea why as they don't interview and they don't rob that many undergrad courses compared to other unis.
I've heard St As and Edinburgh can also be a total nightmare with response times and it's all due to quotas for home students and internationals etc.
Good luck to all your DC. My advice would be to make the gap year count and, if applying to St A, Edinburgh, Durham or particularly LSE, be prepared to wait until at least March. Then, if you hear back earlier, great.