Thanks for the replies everyone, looking at the plane's flying on the routes it looks like the lhr-del leg (B77W) is the international business class with herringbone configuration and the del-bkk is (B738/9) and a regional configuration.

What are peoples thoughts on the difference between Bombay airport & Delhi as via Bombay has slightly better flight times, but reading reviews their airport is a bit more chaotic and need of modernisation plus the connection time of one hour seems a bit tight given the above.