I previously worked in immigration for a number of years. There's lots of ignorance on this thread about how it works and the reality of the situation.
No we shouldn't allow an offshore application in France - not on our own anyway. It would just encourage more numbers to come to France to make the application. And once refused they would still get in a boat anyway and get here.
The ideal solution is a joint approach with all of the EU with assessments being made by UNHCR and each country taking a quota based on population and land mass. And yes off shoring the migrants (not Rwanda but somewhere in the EU) while the consideration (which should be no more than 6 weeks) is made.
The reasons people don't want to stay in France are numerous. Firstly language but also the French police are pretty brutal (and racist) and it is no wonder migrants don't want to stay there. And France made it difficult to take back migrants before Brexit - yes it made it worse as they were pissed off with us but it wasn't easy before. I only saw handfuls of cases being accepted back to France - it could only be done if the asylum seeker had claimed asylum in French and had their biometrics taken. For obvious reasons migrants aren't keen to apply for asylum in France and France are t keen that they do either - they have significant numbers and don't want to add to them.
Yes it is the case that men claim to be kids to try and stay here (some men were clearly older than me and I was mid to late 20s). Yes it's also the case that there are dodgy lawyers - all of us knew the famous company that would get struck off but would then find another brother or uncle without a continual record who managed to get a licence to practise. When I went to court (as the HO rep) I sat at the back of the court and listened until the judge came in - heard lots of useful info that way including the dodgy lawyers telling their clients what to say/not say - something to the detriment of the asylum seeker themselves.
Yes most asylum cases approved. That's because we use the lower standard of proof in this country (reasonable likelihood) whereas the majority of other countries require proof to the civil standard (balance of probabilities).
The French do think we have ourselves to blame for being one of the top countries of choice. They see no point in working with us when we have a vibrant black market, and an over generous welfare system (their views not mine). They think if we sorted that out the pull factors would reduce and they may have a point.
In answer to a pp who asked how we work out who is a genuine asylum seeker - basically via interview. You have to show a well founded fear of persecution so for example just being a woman in Afghanistan wouldn't be enough to secure refugee status unless you were specifically targeted by the Taliban. However, by the same token we couldn't remove a woman back there so even if they were denied refugee status they would stay here under a form of humanitarian protection.