Looking at this -
http://www.ukba.homeoffice.gov.uk/vi...ansit-airside/
I guess -
1. If I have a US / Canadian / Aussie / NZ visa and fly BA - transit through LHR - en route to or from those countries, I can transit without a visa.
2. However, as a citizen of India, I need a DATV (direct airside transit visa, 54 pounds fee, and lots of questions to be answered online, such as about my wife and kids' passports too - though they aren't traveling with me) if I travel to the schengen states using a C visa (visit visa - business or tourist) - even to stay airside between flights. So my best bet to earn oneworld points would be to fly using another OW partner like Finnair, or maybe QR once they join OW - supposedly late 2013.
3. Travel to the Republic of Ireland flying BA needs an Irish visit visa - ok, and after that - not a british DATV, but some other category of visa? [though with no passport control between the UK and ireland - is it that I should just present my Irish visit visa and plane ticket at LHR immigration?]