BTW Dubai to Mumbai is 3 hours, why upgrade for such a short leg?
Because of the passengers he will be sharing the cabin with. He will be travelling economy and lumped in with low class migrant workers whose manners leave a lot to be desired. They don't know how to queue up, toilets will be filthy, bathing and deodorant regarded as optional and they will drink to excess, arguments and fights quite possible.
AVOID flights between the Middle East and the Indian sub continent in economy.
If unable to fly business class, rather choose another transit point. From Manchester a connection via another European airport would be quite possible however a quick look at a well known search engine shows BA as the cheapest airline avoiding the Gulf states.