Haven't seen any official details yet so just speculating at this point, but the China travel ban applies to "any foreign national who was in China during the last 14 days" (except green card holders/diplomats). It'll likely be a similar definition with the EU.

Edit: https://www.dhs.gov/news/2020/03/11/homeland-security-acting... confirmed this (countries in Schengen area)

This is possible. But less likely.

The point of travel restrictions is not to be 100% effective, but instead to reduce the number that travel.

How are you planning to travel to UK by land? It's an island!

The UK is in Europe.