Pressuming its safe to do so, building a false wall using studding and plasterboard to create a cavity between your chimney breast and the new wall, maybe 6 to 8 inches thick , then you can cut out a hole large enough to fit your new tv, and use the cavity to hide your wires.
if heat is an issue, maybe you could make or buy a heat deflector to sit just above your fire to stop the heat rising strait up towards the tv, it should'nt need to stick out too proud.
Again as previously mentioned, i wouldnt touch the brickwork with yours