This does indeed seem like a crazy high number.

Even then, what fraction of all asylum seekers comes via small boats, vs other means? I believe the UK is entirely within its right to send small boats asylum seekers back to France, since it is a safe country. International conventions on asylum seekers state this - you are not entitled to drive thru the whole of Europe then demand asylum specifically in the UK.

I don't want to come across as uncaring, I'm sure there are tragedies that drive people to doing this, that doesn't mean the UK has to also mismanage the process on its side.

From what I've read, about 1/3 of all asylum seekers over the last 7 years arrived via small boat crossings.

Looking forward though, about 90% of those arriving in small boat crossings are currently going on to seek asylum and the average annual cost of supporting an asylum seeker during their claim has risen to an estimated £41k, so for ~30k arrivals this year, the financial cost of not processing these claims promptly could increase that overall annual bill further still.

Also, in the first year of processing, costs may be drawn from the overseas aid budget (which was recently shrunk). This results in possibly 1/5 of the overseas aid budget being used for costs associated with processing asylum claims, which perhaps doesn't match most people's expectations as to what overseas aid should be used for.

I think that's why even though the number of people involved in these crossings is small compared to net migration, it has a big financial impact.

The UK was indeed part of treaty system that meant other states had to "take back" asylum seekers that traveled through them to the UK, but it decided it was in its best interest to quit that a few years ago, so France is a lot less motivated to do that now.