There are very few places where the antipodes (both ends) are on land. The matter was discussed in last night's "Qi".
Some details can be found here: http://www.comedy.co..../tv/qi/episodes/7/12/
The UK is approximately within the square with longitude 0-10 degrees West and latitude 50-60 degrees North. The opposite side of the world is therefore approximately latitude 170-180 degrees East and 50-60 degrees South. You'll see from the link below that this antipodean square is south of New Zealand in open ocean, so the answer is probably that no tunnels would come out on land.
http://www.satsig.net/lat_long.htm
There are very few places where the antipodes (both ends) are on land. The matter was discussed in last night's "Qi".
Some details can be found here: http://www.comedy.co..../tv/qi/episodes/7/12/