I'm looking at travelling from London to Oxford, and then onto Swindon on the same day. I then intend to travel back to London. I'm trying to figure out the cheapest way to do it. Would I be able to buy a Paddington to Swindon return, break my journey at Didcot parkway, buy a return from Didcot to Oxford, then use my initial Paddington to Swindon ticket to continue onto Swindon? Thanks for your help in advance.