This isn’t true. Your landlord has a legal obligation to offer a renew at a fair price (method of calculation is laid out in law). But they have no obligation to actually renew if the leaseholder doesn’t make them. Long leases can absolutely expire, doesn’t happen very often, but it’s certainly not impossible.

I don't understand your point. My understanding is that if there is more than 21 years left on the lease the landlord has zero recourse to not give you a renewal of, I think,50 years, and if you apply for it and they fail to respond it renews automatically.

Most people facing this will engage long before 21 years as well

We’re not actually disagreeing here, I just found your original comment ambiguous.

> give you a renewal of, I think,50 years

Based on what my solicitor told me, I think you get a 999 year lease with peppercorn rent. But I could never find source for that.

So if the leaseholder is bot cooperating it can get very expensive. If the lease goes below 80 years even more so.