This transit without visa issue is extremely important, and I strongly recommend you research it carefully, and not rely on opinions, no matter how sensible they may seem. If they’re wrong, and the traveler lacks a necessary transit visa to get through a country that does not allow travel-without-visa, then the traveler pays the price (being stopped at the border and returned to the home country).
Some countries (Holland, France, Mexico, and no doubt others) allow a traveler to transit their airport provided that the traveler does not exit the security area.
For that to happen, the plane ticket must take the traveler right through to the destination country (no need to exit the security area to book in with a connecting airline), and the luggage must also be checked right through to the destination country.
There are traps. In Madrid, incoming international flights land at one terminal, and if you are continuing on with Air Madrid, you must exit the airport to take a shuttle bus to the next terminal = transit visa needed. Only if you arrived at Madrid on Air Madrid and left the same terminal on Air Madrid would you be able to transit without a visa.
This is why I advise you to confirm all details with the transit county’s embassy in your country.
Getting back to England, I have read in several places that England has stopped the transit-without-visa program. If you normally need a visa to visit the country, then you need a visa to transit it too.
Consult this website:
http://skyteam.com/about/travelhelp/travelinfo.html
Then verify with the embassy.
Good luck!!
It is easier to ship a box than a human being these days.