You may have found the image free online, but in the context of a TARDIS the image of a blue police box is copyrighted (the BBC took the Met to court over it and won) as is Time Lord which you've called your game. The UK doesn't use the fair use clause, it uses fair dealing which is different and only allows non-commercial research or private study, not non-commercial artistic work, which is what a game would be deemed. You can get away with incidental use, but really, a game called timelord, with time travel and a blue police box called the TARDIS? That's not incidental.
I'm just saying you might want to check with them about it. Being in deep water with these people would be a bad idea.